Commit Graph

53 Commits

Author SHA1 Message Date
Rob Norris
213d682967 zdb: show BRT statistics and dump its contents
Same idea as the dedup stats, but for block cloning.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Kay Pedersen <mail@mkwg.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #15541
2023-11-27 13:35:07 -08:00
Mateusz Piotrowski
62ace21a14
zdb: Add missing poolname to -C synopsis
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Mateusz Piotrowski <0mp@FreeBSD.org>
Sponsored-by: Klara Inc.
Closes #15014
2023-06-29 10:54:43 -07:00
Rob Norris
8653f1de48 zdb: add -B option to generate backup stream
This is more-or-less like `zfs send`, but specifying the snapshot by its
objset id for situations where it can't be referenced any other way.

Sponsored-By: Klara, Inc.
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: WHR <msl0000023508@gmail.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #14642
2023-06-05 11:54:42 -07:00
Rob N
163f3d3a1f
zdb: add decryption support
The approach is straightforward: for dataset ops, if a key was offered,
find the encryption root and the various encryption parameters, derive a
wrapping key if necessary, and then unlock the encryption root. After
that all the regular dataset ops will return unencrypted data, and
that's kinda the whole thing.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #11551
Closes #12707
Closes #14503
2023-03-02 13:39:09 -08:00
Rob N
4fe9cc5437
man: note that zdb operates directly on pool storage
A frequent misunderstanding is that zdb accesses the pool through the
kernel or filesystem, leading to confusion particularly when it can't
access something that it seems like it should be able to.

I've seen this confusion recently when zdb couldn't access a pool because
the user didn't have permission to read directly from the block devices,
and when it couldn't show attributes of encrypted files even though the
dataset was unlocked.

The manpage already speaks to another symptom of this, namely that zdb
may "behave erratically" on an active pool; here I'm trying to make that
a little more explicit.

Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #14539
2023-02-28 17:35:33 -08:00
szubersk
b46be903fb Ubuntu 22.04 integration: mancheck
Correct new mandoc errors.
```
STYLE: input text line longer than 80 bytes
STYLE: no blank before trailing delimiter
```

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #14148
2022-11-18 11:26:41 -08:00
наб
a2550c9df9 man: Examples: use subsections instead of lists
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13228
2022-03-28 10:13:13 -07:00
наб
497bf14a4a zdb.8: cleanup
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13093
2022-03-03 10:44:49 -08:00
наб
a737b415d6 man: IO -> I/O; I/Os -> I/O operations again
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13116
2022-02-22 10:55:37 -08:00
Paul Zuchowski
5a4d282f55
Fix problem with zdb -d
zdb -d <pool>/<objset ID> does not work when
other command line arguments are included i.e.
zdb -U <cachefile> -d <pool>/<objset ID>
This change fixes the command line parsing
to handle this situation.  Also fix issue
where zdb -r <dataset> <file> does not handle
the root <dataset> of the pool. Introduce -N
option to force <objset ID> to be interpreted
as a numeric objsetID.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #12845
Closes #12944
2022-01-20 10:28:55 -07:00
Manoj Joseph
6b2e32019e
Long opts for zdb
This change introduces long options for zdb. It updates the usage
message as well to include the long options.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Manoj Joseph <manoj.joseph@delphix.com>
Closes #12818
2022-01-06 10:54:32 -08:00
Rich Ercolani
c5ccbbdcf6
Allow printing special vdev metaslab groups
Sometimes, we'd like to know info about the metaslab groups
on special vdevs too. So let's make -MM do something useful.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12750
2021-11-30 10:26:45 -08:00
наб
f84fe3fc87 Lint most manpages
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12129
2021-06-04 12:48:31 -07:00
Allan Jude
393e69241e
Add zdb -r <dataset> <object-id | file> <output>
While you can use zdb -R poolname vdev:offset:[<lsize>/]<psize>[:flags] 
to extract individual DVAs from a vdev, it would be handy for be able 
copy an entire file out of the pool.

Given a file or object number, add support to copy the contents to a 
file. Useful for debugging and recovery.

Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Allan Jude <allan@klarasystems.com>
Closes #11027
2021-01-27 21:36:01 -08:00
Ryan Moeller
6706552ea6
Remove hard coded "Linux" OS from manpages
The recommended practice for `.Os` on FreeBSD is to not specify any
arguments.  The correct OS name is used automatically.

Oddly enough, on the Linux distro I tested this on (CentOS 7), the man
pager defaulted to displaying "BSD" as the OS rather than "Linux".  To
accommodate this, tack " Linux" back on in an install hook on Linux.
This is much simpler than removing it for FreeBSD when vendored in the
base system.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10760
2020-08-21 11:55:47 -07:00
Matthew Ahrens
6774931dfa
Extend zdb to print inconsistencies in livelists and metaslabs
Livelists and spacemaps are data structures that are logs of allocations
and frees.  Livelists entries are block pointers (blkptr_t). Spacemaps
entries are ranges of numbers, most often used as to track
allocated/freed regions of metaslabs/vdevs.

These data structures can become self-inconsistent, for example if a
block or range can be "double allocated" (two allocation records without
an intervening free) or "double freed" (two free records without an
intervening allocation).

ZDB (as well as zfs running in the kernel) can detect these
inconsistencies when loading livelists and metaslab.  However, it
generally halts processing when the error is detected.

When analyzing an on-disk problem, we often want to know the entire set
of inconsistencies, which is not possible with the current behavior.
This commit adds a new flag, `zdb -y`, which analyzes the livelist and
metaslab data structures and displays all of their inconsistencies.
Note that this is different from the leak detection performed by
`zdb -b`, which checks for inconsistencies between the spacemaps and the
tree of block pointers, but assumes the spacemaps are self-consistent.

The specific checks added are:

Verify livelists by iterating through each sublivelists and:
- report leftover FREEs
- report double ALLOCs and double FREEs
- record leftover ALLOCs together with their TXG [see Cross Check]

Verify spacemaps by iterating over each metaslab and:
- iterate over spacemap and then the metaslab's entries in the
  spacemap log, then report any double FREEs and double ALLOCs

Verify that livelists are consistenet with spacemaps.  The space
referenced by livelists (after using the FREE's to cancel out
corresponding ALLOCs) should be allocated, according to the spacemaps.

Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Sara Hartse <sara.hartse@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-66031
Closes #10515
2020-07-14 17:51:05 -07:00
Andrea Gelmini
dd4bc569b9
Fix typos
Correct various typos in the comments and tests.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #10423
2020-06-09 21:24:09 -07:00
George Amanakis
657fd33bcf
Improvements on persistent L2ARC
Functional changes:

We implement refcounts of log blocks and their aligned size on the
cache device along with two corresponding arcstats. The refcounts are
reflected in the header of the device and provide valuable information
as to whether log blocks are accounted for correctly. These are
dynamically adjusted as log blocks are committed/evicted. zdb also uses
this information in the device header and compares it to the
corresponding values as reported by dump_l2arc_log_blocks() which
emulates l2arc_rebuild(). If the refcounts saved in the device header
report higher values, zdb exits with an error. For this feature to work
correctly there should be no active writes on the device. This is also
employed in the tests of persistent L2ARC. We extend the structure of
the cache device header by adding the two new variables mirroring the
refcounts after the existing variables to preserve backward
compatibility in terms of persistent L2ARC.

1) a new arcstat "l2_log_blk_asize" and refcount "l2ad_lb_asize" which
   reflect the total aligned size of log blocks on the device. This is
   also reflected in the header of the cache device as "dh_lb_asize".
2) a new arcstat "l2arc_log_blk_count" and refcount "l2ad_lb_count"
   which reflect the total number of L2ARC log blocks present on cache
   devices.  It is also reflected in the header of the cache device as
   "dh_lb_count".

In l2arc_rebuild_vdev() if the amount of committed log entries in a log
block is 0 and the device header is valid we update the device header.
This will facilitate trimming of the whole device in this case when
TRIM for L2ARC is implemented.

Improve loop protection in l2arc_rebuild() by using the starting offset
of the payload of each log block instead of the starting offset of the
log block.

If the zio in l2arc_write_buffers() fails, restore the lbps array in the
header of the device to its previous state in l2arc_write_done().

If l2arc_rebuild() ends the rebuild process without restoring any L2ARC
log blocks in ARC and without any other error, this means that the lbps
array in the header is pointing to non-existent or invalid log blocks.
Reset the device header in this case.

In l2arc_rebuild() change the zfs_dbgmsg messages to
spa_history_log_internal() making them user visible with zpool history
command.

Non-functional changes:

Make the first test in persistent L2ARC use `zdb -lll` to increase
coverage in `zdb.c`.

Rename psize with asize when referring to log blocks, since
L2ARC_SET_PSIZE stores the vdev aligned size for log blocks. Also
rename dh_log_blk_entries to dh_log_entries to make it clear that
it is a mirror of l2ad_log_entries. Added comments for both changes.

Fix inaccurate comments for example in l2arc_log_blk_restore().

Add asserts at the end in l2arc_evict() and l2arc_write_buffers().

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Closes #10228
2020-05-07 16:34:03 -07:00
George Amanakis
77f6826b83
Persistent L2ARC
This commit makes the L2ARC persistent across reboots. We implement
a light-weight persistent L2ARC metadata structure that allows L2ARC
contents to be recovered after a reboot. This significantly eases the
impact a reboot has on read performance on systems with large caches.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Saso Kiselkov <skiselkov@gmail.com>
Co-authored-by: Jorgen Lundman <lundman@lundman.net>
Co-authored-by: George Amanakis <gamanakis@gmail.com>
Ported-by: Yuxuan Shui <yshuiv7@gmail.com>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Closes #925 
Closes #1823 
Closes #2672 
Closes #3744 
Closes #9582
2020-04-10 10:33:35 -07:00
Paul Zuchowski
bc67cba7c0
Fix zdb -R with 'b' flag
zdb -R :b fails due to the indirect block being compressed,
and the 'b' and 'd' flag not working in tandem when specified.
Fix the flag parsing code and create a zfs test for zdb -R
block display.  Also fix the zio flags where the dotted notation
for the vdev portion of DVA (i.e. 0.0:offset:length) fails.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #9640
Closes #9729
2020-02-10 14:00:05 -08:00
Ned Bass
a3403164d7 zdb: add support for object ranges for zdb -d
Allow a range of object identifiers to dump with -d. This may
be useful when dumping a large dataset and you want to break
it up into multiple phases, or to resume where a previous scan
left off. Object type selection flags are supported to reduce
the performance overhead of verbosely dumping unwanted objects,
and to reduce the amount of post-processing work needed to
filter out unwanted objects from zdb output.

This change extends existing syntax in a backward-compatible
way. That is, the base case of a range is to specify a single
object identifier to dump. Ranges and object identifiers can
be intermixed as command line parameters.

Usage synopsis:

    Object ranges take the form <start>:<end>[:<flags>]
        start    Starting object number
        end      Ending object number, or -1 for no upper bound
        flags    Optional flags to select object types:
         A    All objects (this is the default)
         d    ZFS directories
         f    ZFS files
         m    SPA space maps
         z    ZAPs
         -    Negate effect of next flag

Examples:

 # Dump all file objects
 zdb -dd tank/fish 0👎f

 # Dump all file and directory objects
 zdb -dd tank/fish 0👎fd

 # Dump all types except file and directory objects
 zdb -dd tank/fish 0👎A-f-d

 # Dump object IDs in a specific range
 zdb -dd tank/fish 1000:2000

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Paul Zuchowski <pzuchowski@datto.com>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Closes #9832
2020-01-24 11:00:46 -08:00
Paul Zuchowski
f12e42cccf zdb -d should accept the numeric objset id
As an alternative to the dataset name, zdb now allows the decimal 
or hexadecimal objset ID to be specified.  When permanent errors
are reported as 2 hexadecimal numbers (objset ID : object ID) in 
zpool status; you can now use 'zdb <pool>[/objset ID] object' to
determine the names of the objset and object which have the error.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #9733
2020-01-16 09:22:49 -08:00
Paul Zuchowski
f0bf435176 zio_decompress_data always ASSERTs successful decompression
This interferes with zdb_read_block trying all the decompression
algorithms when the 'd' flag is specified, as some are
expected to fail.  Also control the output when guessing
algorithms, try the more common compression types first, allow
specifying lsize/psize, and fix an uninitialized variable.

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #9612 
Closes #9630
2019-12-10 15:51:58 -08:00
Paul Zuchowski
894f6696b4 Add display of checksums to zdb -R
The function zdb_read_block (zdb -R) was always intended to have a :c 
flag which would read the DVA and length supplied by the user, and 
display the checksum. Since we don't know which checksum goes with 
the data, we should calculate and display them all.

For each checksum in the table, read in the data at the supplied 
DVA:length, calculate the checksum, and display it. Update the man 
page and create a zfs test for the new feature.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #9607
2019-11-27 10:08:18 -08:00
Andrea Gelmini
ac3d4d0cf6 Fix typos in man/
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #9233
2019-08-30 09:41:35 -07:00
Serapheim Dimitropoulos
93e28d661e Log Spacemap Project
= Motivation

At Delphix we've seen a lot of customer systems where fragmentation
is over 75% and random writes take a performance hit because a lot
of time is spend on I/Os that update on-disk space accounting metadata.
Specifically, we seen cases where 20% to 40% of sync time is spend
after sync pass 1 and ~30% of the I/Os on the system is spent updating
spacemaps.

The problem is that these pools have existed long enough that we've
touched almost every metaslab at least once, and random writes
scatter frees across all metaslabs every TXG, thus appending to
their spacemaps and resulting in many I/Os. To give an example,
assuming that every VDEV has 200 metaslabs and our writes fit within
a single spacemap block (generally 4K) we have 200 I/Os. Then if we
assume 2 levels of indirection, we need 400 additional I/Os and
since we are talking about metadata for which we keep 2 extra copies
for redundancy we need to triple that number, leading to a total of
1800 I/Os per VDEV every TXG.

We could try and decrease the number of metaslabs so we have less
I/Os per TXG but then each metaslab would cover a wider range on
disk and thus would take more time to be loaded in memory from disk.
In addition, after it's loaded, it's range tree would consume more
memory.

Another idea would be to just increase the spacemap block size
which would allow us to fit more entries within an I/O block
resulting in fewer I/Os per metaslab and a speedup in loading time.
The problem is still that we don't deal with the number of I/Os
going up as the number of metaslabs is increasing and the fact
is that we generally write a lot to a few metaslabs and a little
to the rest of them. Thus, just increasing the block size would
actually waste bandwidth because we won't be utilizing our bigger
block size.

= About this patch

This patch introduces the Log Spacemap project which provides the
solution to the above problem while taking into account all the
aforementioned tradeoffs. The details on how it achieves that can
be found in the references sections below and in the code (see
Big Theory Statement in spa_log_spacemap.c).

Even though the change is fairly constraint within the metaslab
and lower-level SPA codepaths, there is a side-change that is
user-facing. The change is that VDEV IDs from VDEV holes will no
longer be reused. To give some background and reasoning for this,
when a log device is removed and its VDEV structure was replaced
with a hole (or was compacted; if at the end of the vdev array),
its vdev_id could be reused by devices added after that. Now
with the pool-wide space maps recording the vdev ID, this behavior
can cause problems (e.g. is this entry referring to a segment in
the new vdev or the removed log?). Thus, to simplify things the
ID reuse behavior is gone and now vdev IDs for top-level vdevs
are truly unique within a pool.

= Testing

The illumos implementation of this feature has been used internally
for a year and has been in production for ~6 months. For this patch
specifically there don't seem to be any regressions introduced to
ZTS and I have been running zloop for a week without any related
problems.

= Performance Analysis (Linux Specific)

All performance results and analysis for illumos can be found in
the links of the references. Redoing the same experiments in Linux
gave similar results. Below are the specifics of the Linux run.

After the pool reached stable state the percentage of the time
spent in pass 1 per TXG was 64% on average for the stock bits
while the log spacemap bits stayed at 95% during the experiment
(graph: sdimitro.github.io/img/linux-lsm/PercOfSyncInPassOne.png).

Sync times per TXG were 37.6 seconds on average for the stock
bits and 22.7 seconds for the log spacemap bits (related graph:
sdimitro.github.io/img/linux-lsm/SyncTimePerTXG.png). As a result
the log spacemap bits were able to push more TXGs, which is also
the reason why all graphs quantified per TXG have more entries for
the log spacemap bits.

Another interesting aspect in terms of txg syncs is that the stock
bits had 22% of their TXGs reach sync pass 7, 55% reach sync pass 8,
and 20% reach 9. The log space map bits reached sync pass 4 in 79%
of their TXGs, sync pass 7 in 19%, and sync pass 8 at 1%. This
emphasizes the fact that not only we spend less time on metadata
but we also iterate less times to convergence in spa_sync() dirtying
objects.
[related graphs:
stock- sdimitro.github.io/img/linux-lsm/NumberOfPassesPerTXGStock.png
lsm- sdimitro.github.io/img/linux-lsm/NumberOfPassesPerTXGLSM.png]

Finally, the improvement in IOPs that the userland gains from the
change is approximately 40%. There is a consistent win in IOPS as
you can see from the graphs below but the absolute amount of
improvement that the log spacemap gives varies within each minute
interval.
sdimitro.github.io/img/linux-lsm/StockVsLog3Days.png
sdimitro.github.io/img/linux-lsm/StockVsLog10Hours.png

= Porting to Other Platforms

For people that want to port this commit to other platforms below
is a list of ZoL commits that this patch depends on:

Make zdb results for checkpoint tests consistent
db587941c5

Update vdev_is_spacemap_addressable() for new spacemap encoding
419ba59145

Simplify spa_sync by breaking it up to smaller functions
8dc2197b7b

Factor metaslab_load_wait() in metaslab_load()
b194fab0fb

Rename range_tree_verify to range_tree_verify_not_present
df72b8bebe

Change target size of metaslabs from 256GB to 16GB
c853f382db

zdb -L should skip leak detection altogether
21e7cf5da8

vs_alloc can underflow in L2ARC vdevs
7558997d2f

Simplify log vdev removal code
6c926f426a

Get rid of space_map_update() for ms_synced_length
425d3237ee

Introduce auxiliary metaslab histograms
928e8ad47d

Error path in metaslab_load_impl() forgets to drop ms_sync_lock
8eef997679

= References

Background, Motivation, and Internals of the Feature
- OpenZFS 2017 Presentation:
youtu.be/jj2IxRkl5bQ
- Slides:
slideshare.net/SerapheimNikolaosDim/zfs-log-spacemaps-project

Flushing Algorithm Internals & Performance Results
(Illumos Specific)
- Blogpost:
sdimitro.github.io/post/zfs-lsm-flushing/
- OpenZFS 2018 Presentation:
youtu.be/x6D2dHRjkxw
- Slides:
slideshare.net/SerapheimNikolaosDim/zfs-log-spacemap-flushing-algorithm

Upstream Delphix Issues:
DLPX-51539, DLPX-59659, DLPX-57783, DLPX-61438, DLPX-41227, DLPX-59320
DLPX-63385

Reviewed-by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #8442
2019-07-16 10:11:49 -07:00
Richard Laager
e7ce9759ac Correct man page dates
Various changes (many by me) have been made to the man pages without
bumping their dates.  I have now corrected them based on the last commit
to each file.  I also added the script I used to make these changes.

Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Laager <rlaager@wiktel.com>
Closes #8710
2019-05-08 10:59:32 -07:00
Richard Laager
c349137a7e Update zdb.8's fsck reference
On Linux, this is in man section 8, not 1M.  Also, there is no fsdb on
Linux, so I removed that.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Laager <rlaager@wiktel.com>
Closes #8626
2019-04-16 10:01:38 -07:00
Serapheim Dimitropoulos
21e7cf5da8 zdb -L should skip leak detection altogether
Currently the point of -L option in zdb is to  disable leak
tracing and the loading of space maps because they are expensive,
yet still do leak detection in terms of space. Unfortunately,
there is a scenario where this is a lie. If we are using zdb -L
on a pool where a vdev is being removed, zdb_claim_removing()
will open the metaslab space maps of that device.

This patch makes it so zdb -L skips leak detection altogether
and ensures that no space maps are loaded.

Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #8335
2019-01-30 09:54:27 -08:00
Brian Behlendorf
64bdf63f5c
ztest: split block reconstruction
Increase the default allowed number of reconstruction attempts.
There's not an exact right number for this setting.  It needs
to be set large enough to cover any realistic failure scenarios
and small enough to avoid stalling the IO pipeline and invoking
the dead man detection.

The current value of 256 was empirically determined to be too
low based on multi-day runs of ztest.  The fault injection code
would inject more damage than could be reconstructed given the
relatively small number of attempts.  However, in all observed
cases the block could be reconstructed using a slightly higher
limit.

Based on local testing increasing the default value to 4096 was
determined to strike the best balance.  Checking all combinations
takes less than 10s in the worst case, and has so far eliminated
the vast majority of false positives detected by ztest.  This
delay is roughly on par with how long retries may be performed
to a misbehaving HDD and was deemed to be reasonable.  Better to
err on the side of a brief delay rather than fail to reconstruct
the data.

Lastly, the -Y flag has been added to zdb to make it easy to try all
possible combinations when performing split block reconstruction.
For badly damaged blocks with 18 splits, they can be fully enumerated
within a few minutes.  This has been done to ensure permanent errors
are never incorrectly reported when ztest verifies the pool with zdb.

Reviewed by: Tom Caputi <tcaputi@datto.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Serapheim Dimitropoulos <serapheim@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #8271
2019-01-16 14:10:02 -08:00
Serapheim Dimitropoulos
d2734cce68 OpenZFS 9166 - zfs storage pool checkpoint
Details about the motivation of this feature and its usage can
be found in this blogpost:

    https://sdimitro.github.io/post/zpool-checkpoint/

A lightning talk of this feature can be found here:
https://www.youtube.com/watch?v=fPQA8K40jAM

Implementation details can be found in big block comment of
spa_checkpoint.c

Side-changes that are relevant to this commit but not explained
elsewhere:

* renames members of "struct metaslab trees to be shorter without
  losing meaning

* space_map_{alloc,truncate}() accept a block size as a
  parameter. The reason is that in the current state all space
  maps that we allocate through the DMU use a global tunable
  (space_map_blksz) which defauls to 4KB. This is ok for metaslab
  space maps in terms of bandwirdth since they are scattered all
  over the disk. But for other space maps this default is probably
  not what we want. Examples are device removal's vdev_obsolete_sm
  or vdev_chedkpoint_sm from this review. Both of these have a
  1:1 relationship with each vdev and could benefit from a bigger
  block size.

Porting notes:

* The part of dsl_scan_sync() which handles async destroys has
  been moved into the new dsl_process_async_destroys() function.

* Remove "VERIFY(!(flags & FWRITE))" in "kernel.c" so zhack can write
  to block device backed pools.

* ZTS:
  * Fix get_txg() in zpool_sync_001_pos due to "checkpoint_txg".

  * Don't use large dd block sizes on /dev/urandom under Linux in
    checkpoint_capacity.

  * Adopt Delphix-OS's setting of 4 (spa_asize_inflation =
    SPA_DVAS_PER_BP + 1) for the checkpoint_capacity test to speed
    its attempts to fill the pool

  * Create the base and nested pools with sync=disabled to speed up
    the "setup" phase.

  * Clear labels in test pool between checkpoint tests to avoid
    duplicate pool issues.

  * The import_rewind_device_replaced test has been marked as "known
    to fail" for the reasons listed in its DISCLAIMER.

  * New module parameters:

      zfs_spa_discard_memory_limit,
      zfs_remove_max_bytes_pause (not documented - debugging only)
      vdev_max_ms_count (formerly metaslabs_per_vdev)
      vdev_min_ms_count

Authored by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Richard Lowe <richlowe@richlowe.net>
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Tim Chase <tim@chase2k.com>

OpenZFS-issue: https://illumos.org/issues/9166
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/7159fdb8
Closes #7570
2018-06-26 10:07:42 -07:00
Chunwei Chen
950e17c215 Fix zdb -R decompression
There are some issues in the zdb -R decompression implementation.

The first is that ZLE can easily decompress non-ZLE streams. So we add
ZDB_NO_ZLE env to make zdb skip ZLE.

The second is the random bytes appended to pabd, pbuf2 stuff. This serve
no purpose at all, those bytes shouldn't be read during decompression
anyway. Instead, we randomize lbuf2, so that we can make sure
decompression fill exactly to lsize by bcmp lbuf and lbuf2.

The last one is the condition to detect fail is wrong.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Closes #7099
Closes #4984
2018-02-09 10:11:02 -08:00
Giuseppe Di Natale
d7323e79a6 OpenZFS 8547 - update mandoc to 1.14.3
Authored by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/8547
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/c66b804
Closes #6549
2017-08-24 10:30:42 -07:00
Matthew Ahrens
a896468c78 OpenZFS 8067 - zdb should be able to dump literal embedded block pointer
Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Alex Reece <alex@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@gmail.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/8067
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/8173085
Closes #6319
2017-07-07 11:28:01 -07:00
Richard Yao
066753103f OpenZFS 6392 - zdb: introduce -V for verbatim import
Authored by: Richard Yao <ryao@gentoo.org>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Yuri Pankov <yuri.pankov@gmail.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

Porting Notes:
  This was already implemented in ZFS on Linux. This patch
  is to resolved the deltas present in our version.

OpenZFS-issue: https://www.illumos.org/issues/6392
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/9bb97de
Closes #6020
2017-04-18 09:50:15 -07:00
Brian Behlendorf
a44e7faa6c OpenZFS 6410 - teach zdb to perform object lookups by path
Authored by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Will Andrews <will@freebsd.org>
Approved by: Dan McDonald <danmcd@omniti.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting Notes:
- Replaced zdb.8 with upstream mdoc zdb.1m version.  Updated to
  include Linux specific features: -V verbatium imports and
  improved label printing (-u, and -l).
- Minor changes to `zdb -h` output to honor 80 character limit.

OpenZFS-issue: https://www.illumos.org/issues/6410
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/ed61ec1
Closes #6006
2017-04-13 09:40:56 -07:00
Olaf Faaland
3c9e0d673e Dump unique configurations and Uberblocks in zdb -lu
For zdb -l, detect when the configuration nvlist in some label l (l>0)
is the same as a configuration already dumped.  If so, do not dump it.

Make a similar check when dumping Uberblocks for zdb -lu.  Check whether
a label already dumped contains an identical Uberblock.  If so, do not
dump the Uberblock.

When dumping a configuration or Uberblock, state which labels it is
found in (0-3), for example: labels = 1 2 3

Detecting redundant uberblocks or configurations is accomplished by
calculating checksums of the uberblocks and the packed nvlists
containing the configuration.

If there is nothing unique to be dumped for a label (ie the
configuration and uberblocks have checksums matching those already
dumped) print nothing for that label.

With additional l's or u's, increase verbosity as follows:

-l      Dump each unique configuration only once.
        Indicate which labels it appears in.
-ll     In addition, dump label space usage stats.
-lll    Dump every configuration, unique or not.

-u      Dump each unique, valid, uberblock only once.
        Indicate which labels it appears in.
-uu     In addition, state which slots are invalid.
-uuu    Dump every uberblock, unique or not.
-uuuu   Dump the uberblock blockpointer (used to be -uuu)

Make exit values conform to the manual page.  Failing to unpack a
configuration nvlist is considered an error, as well as failing to open
or read from the device.

Add three tests, zdb_00{3,4,5}_pos to verify the above functionality.

An example of the output:
	------------------------------------
	LABEL 0
	------------------------------------
	    version: 5000
	    name: 'pool'
	    state: 1
	    txg: 880
	    < ... redacted ... >
	    features_for_read:
		com.delphix:hole_birth
		com.delphix:embedded_data
	    labels = 0
	    Uberblock[0]
		magic = 0000000000bab10c
		version = 5000
		txg = 0
		guid_sum = 3038694082047428541
		timestamp = 1487715500 UTC = Tue Feb 21 14:18:20 2017
		labels = 0 1 2 3
	    Uberblock[4]
		magic = 0000000000bab10c
		version = 5000
		txg = 772
		guid_sum = 9045970794941528051
		timestamp = 1487727291 UTC = Tue Feb 21 17:34:51 2017
		labels = 0
	    < ... redacted ... >
	------------------------------------
	LABEL 1
	------------------------------------
	    version: 5000
	    name: 'pool'
	    state: 1
	    txg: 14
	    < ... redacted ... >
		com.delphix:embedded_data
	    labels = 1 2 3
	    Uberblock[4]
		magic = 0000000000bab10c
		version = 5000
		txg = 4
		guid_sum = 7793930272573252584
		timestamp = 1487727521 UTC = Tue Feb 21 17:38:41 2017
		labels = 1 2 3
	    < ... redacted ... >

Reviewed-by: Tim Chase <tim@chase2k.com>
Reviewed-by: Don Brady <don.brady@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #5738
2017-03-06 16:01:45 -08:00
Don Brady
35a357a9ef OpenZFS 6866 - zdb -l non-zero status if no label
Authored by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Ported-by: Don Brady <don.brady@intel.com>

OpenZFS-issue: https://www.illumos.org/issues/6866
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/3e4fae5
Closes #5730 

Porting Notes:
- Omitted the illumos-specific `/dev/dsk` and `/dev/rdsk`
path conversions since they don't apply on linux.
2017-02-03 14:18:28 -08:00
George Melikov
ed828c0c37 OpenZFS 7280 - Allow changing global libzpool variables in zdb and ztest through command line
Authored by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7280
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/0e60744
Closes #5676
2017-01-31 10:13:10 -08:00
George Melikov
fa603f8233 OpenZFS 7277 - zdb should be able to print zfs_dbgmsg's
Porting notes:
- 'zfs_dbgmsg_print()' reintroduced to userspace.

Authored by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Igor Kozhukhov <ikozhukhov@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7277
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/29bdd2f
Closes #5684
2017-01-28 12:16:43 -08:00
Matthew Ahrens
9867e8be2a Illumos 4891 - want zdb option to dump all metadata
4891 want zdb option to dump all metadata
Reviewed by: Sonu Pillai <sonu.pillai@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Garrett D'Amore <garrett@damore.org>

We'd like a way for zdb to dump metadata in a machine-readable
format, so that we can bring that back from a customer site for
in-house diagnosis.  Think of it as a crash dump for zpools,
which can be used for post-mortem analysis of a malfunctioning
pool

References:
  https://www.illumos.org/issues/4891
  https://github.com/illumos/illumos-gate/commit/df15e41

Porting notes:
- [cmd/zdb/zdb.c]
  - a5778ea zdb: Introduce -V for verbatim import
  - In main() getopt 'opt' variable removed and the code was
    brought back in line with illumos.
- [lib/libzpool/kernel.c]
  - 1e33ac1 Fix Solaris thread dependency by using pthreads
  - f0e324f Update utsname support
  - 4d58b69 Fix vn_open/vn_rdwr error handling
  - In vn_open() allocate 'dumppath' on heap instead of stack
  - Properly handle 'dump_fd == -1' error path
  - Free 'realpath' after added vn_dumpdir_code block

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2016-01-11 11:36:54 -08:00
Ned Bass
6b4e21c60e Man page white space and spelling corrections
Correct some misspelled words and grammatical errors, and remove
trailing white space in the man pages.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4115
2015-12-18 13:33:37 -08:00
Tim Chase
b1b85c8772 Zdb should be able to open the root dataset
If the pool/dataset command-line argument is specified with a trailing
slash, for example, "tank/", it is interpreted as the root dataset.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3415
2015-05-15 10:52:46 -07:00
Turbo Fredriksson
71bd064555 Document environment variables for zdb, zfs, zinject and zpool.
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2691
2014-09-18 15:01:03 -07:00
George Wilson
f3a7f6610f Illumos 4976-4984 - metaslab improvements
4976 zfs should only avoid writing to a failing non-redundant top-level vdev
4978 ztest fails in get_metaslab_refcount()
4979 extend free space histogram to device and pool
4980 metaslabs should have a fragmentation metric
4981 remove fragmented ops vector from block allocator
4982 space_map object should proactively upgrade when feature is enabled
4983 need to collect metaslab information via mdb
4984 device selection should use fragmentation metric
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Adam Leventhal <adam.leventhal@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
  https://www.illumos.org/issues/4976
  https://www.illumos.org/issues/4978
  https://www.illumos.org/issues/4979
  https://www.illumos.org/issues/4980
  https://www.illumos.org/issues/4981
  https://www.illumos.org/issues/4982
  https://www.illumos.org/issues/4983
  https://www.illumos.org/issues/4984
  https://github.com/illumos/illumos-gate/commit/2e4c998

Notes:
    The "zdb -M" option has been re-tasked to display the new metaslab
    fragmentation metric and the new "zdb -I" option is used to control
    the maximum number of in-flight I/Os.

    The new fragmentation metric is derived from the space map histogram
    which has been rolled up to the vdev and pool level and is presented
    to the user via "zpool list".

    Add a number of module parameters related to the new metaslab weighting
    logic.

Ported by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2595
2014-08-18 08:40:49 -07:00
Richard Yao
a5778ea242 zdb: Introduce -V for verbatim import
When given a pool name via -e, zdb would attempt an import. If it
failed, then it would attempt a verbatim import. This behavior is
not always desirable so a -V switch is added to zdb to control the
behavior. When specified, a verbatim import is done. Otherwise,
the behavior is as it was previously, except no verbatim import
is done on failure.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2372
2014-07-17 11:40:32 -07:00
Tim Chase
2e2ddc30b4 Dedup-related documentation additions for zpool and zdb.
Document the "-D" and "-T" options and the optional interval
and count or "zpool status".

Also for zpool's man page, use a consistent order for the
various "-T" options to match the program's help output.

Document the effect of additional "-D" options for zdb.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1786
2013-10-22 10:08:51 -07:00
George Wilson
5853fe790d Illumos #3306, #3321
3306 zdb should be able to issue reads in parallel
3321 'zpool reopen' command should be documented in the man
     page and help

Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by: Christopher Siden <chris.siden@delphix.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
  illumos/illumos-gate@31d7e8fa33
  https://www.illumos.org/issues/3306
  https://www.illumos.org/issues/3321

The vdev_file.c implementation in this patch diverges significantly
from the upstream version.  For consistenty with the vdev_disk.c
code the upstream version leverages the Illumos bio interfaces.
This makes sense for Illumos but not for ZoL for two reasons.

1) The vdev_disk.c code in ZoL has been rewritten to use the
   Linux block device interfaces which differ significantly
   from those in Illumos.  Therefore, updating the vdev_file.c
   to use the Illumos interfaces doesn't get you consistency
   with vdev_disk.c.

2) Using the upstream patch as is would requiring implementing
   compatibility code for those Solaris block device interfaces
   in user and kernel space.  That additional complexity could
   lead to confusion and doesn't buy us anything.

For these reasons I've opted to simply move the existing vn_rdwr()
as is in to the taskq function.  This has the advantage of being
low risk and easy to understand.  Moving the vn_rdwr() function
in to its own taskq thread also neatly avoids the possibility of
a stack overflow.

Finally, because of the additional work which is being handled by
the free taskq the number of threads has been increased.  The
thread count under Illumos defaults to 100 but was decreased to 2
in commit 08d08e due to contention.  We increase it to 8 until
the contention can be address by porting Illumos #3581.

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1354
2013-05-03 16:53:52 -07:00
Brian Behlendorf
2016ff96d1 Fix zdb.8 macro warning
Detected by rpmlint the 'rpool/export/home' section was being
interpretted by troff as an undefined macro.  This resulted
in the 'rpool/export/home' output being omitted from 'man zdb'.

This was caused by starting the line with a ' character.  By
moving the 'in' down to the next line we're able to fix it.

  zfs.x86_64: W: manual-page-warning /usr/share/man/man8/zdb.8.gz
  450: warning: macro `rpool/export/home'' not defined

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2013-03-06 15:46:41 -08:00
Richard Lowe
dd4769adc0 Illumos #2088 zdb could use a reasonable manual page
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Reviewed by: George Wilson <gwilson@zfsmail.com>
Reviewed by: Steve Gonczi <gonczi@comcast.net>
Reviewed by: Richard Elling <richard.elling@richardelling.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
      https://www.illumos.org/issues/2088

Ported by: Cyril Plisko <cyril.plisko@mountall.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #682
2012-09-18 09:09:13 -07:00