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mirror_zfs/man/man8/zpool-events.8
Brian Atkinson a10e552b99
Adding Direct IO Support 
Adding O_DIRECT support to ZFS to bypass the ARC for writes/reads.

O_DIRECT support in ZFS will always ensure there is coherency between
buffered and O_DIRECT IO requests. This ensures that all IO requests,
whether buffered or direct, will see the same file contents at all
times. Just as in other FS's , O_DIRECT does not imply O_SYNC. While
data is written directly to VDEV disks, metadata will not be synced
until the associated  TXG is synced.
For both O_DIRECT read and write request the offset and request sizes,
at a minimum, must be PAGE_SIZE aligned. In the event they are not,
then EINVAL is returned unless the direct property is set to always (see
below).

For O_DIRECT writes:
The request also must be block aligned (recordsize) or the write
request will take the normal (buffered) write path. In the event that
request is block aligned and a cached copy of the buffer in the ARC,
then it will be discarded from the ARC forcing all further reads to
retrieve the data from disk.

For O_DIRECT reads:
The only alignment restrictions are PAGE_SIZE alignment. In the event
that the requested data is in buffered (in the ARC) it will just be
copied from the ARC into the user buffer.

For both O_DIRECT writes and reads the O_DIRECT flag will be ignored in
the event that file contents are mmap'ed. In this case, all requests
that are at least PAGE_SIZE aligned will just fall back to the buffered
paths. If the request however is not PAGE_SIZE aligned, EINVAL will
be returned as always regardless if the file's contents are mmap'ed.

Since O_DIRECT writes go through the normal ZIO pipeline, the
following operations are supported just as with normal buffered writes:
Checksum
Compression
Encryption
Erasure Coding
There is one caveat for the data integrity of O_DIRECT writes that is
distinct for each of the OS's supported by ZFS.
FreeBSD - FreeBSD is able to place user pages under write protection so
          any data in the user buffers and written directly down to the
	  VDEV disks is guaranteed to not change. There is no concern
	  with data integrity and O_DIRECT writes.
Linux - Linux is not able to place anonymous user pages under write
        protection. Because of this, if the user decides to manipulate
	the page contents while the write operation is occurring, data
	integrity can not be guaranteed. However, there is a module
	parameter `zfs_vdev_direct_write_verify` that controls the
	if a O_DIRECT writes that can occur to a top-level VDEV before
	a checksum verify is run before the contents of the I/O buffer
        are committed to disk. In the event of a checksum verification
	failure the write will return EIO. The number of O_DIRECT write
	checksum verification errors can be observed by doing
	`zpool status -d`, which will list all verification errors that
	have occurred on a top-level VDEV. Along with `zpool status`, a
	ZED event will be issues as `dio_verify` when a checksum
	verification error occurs.

ZVOLs and dedup is not currently supported with Direct I/O.

A new dataset property `direct` has been added with the following 3
allowable values:
disabled - Accepts O_DIRECT flag, but silently ignores it and treats
	   the request as a buffered IO request.
standard - Follows the alignment restrictions  outlined above for
	   write/read IO requests when the O_DIRECT flag is used.
always   - Treats every write/read IO request as though it passed
           O_DIRECT and will do O_DIRECT if the alignment restrictions
	   are met otherwise will redirect through the ARC. This
	   property will not allow a request to fail.

There is also a module parameter zfs_dio_enabled that can be used to
force all reads and writes through the ARC. By setting this module
parameter to 0, it mimics as if the  direct dataset property is set to
disabled.

Reviewed-by: Brian Behlendorf <behlendorf@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Co-authored-by: Mark Maybee <mark.maybee@delphix.com>
Co-authored-by: Matt Macy <mmacy@FreeBSD.org>
Co-authored-by: Brian Behlendorf <behlendorf@llnl.gov>
Closes #10018
2024-09-14 13:47:59 -07:00

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.\" Copyright (c) 2012, 2018 by Delphix. All rights reserved.
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.Dd February 28, 2024
.Dt ZPOOL-EVENTS 8
.Os
.
.Sh NAME
.Nm zpool-events
.Nd list recent events generated by kernel
.Sh SYNOPSIS
.Nm zpool
.Cm events
.Op Fl vHf
.Op Ar pool
.Nm zpool
.Cm events
.Fl c
.
.Sh DESCRIPTION
Lists all recent events generated by the ZFS kernel modules.
These events are consumed by the
.Xr zed 8
and used to automate administrative tasks such as replacing a failed device
with a hot spare.
For more information about the subclasses and event payloads
that can be generated see
.Sx EVENTS
and the following sections.
.
.Sh OPTIONS
.Bl -tag -compact -width Ds
.It Fl c
Clear all previous events.
.It Fl f
Follow mode.
.It Fl H
Scripted mode.
Do not display headers, and separate fields by a
single tab instead of arbitrary space.
.It Fl v
Print the entire payload for each event.
.El
.
.Sh EVENTS
These are the different event subclasses.
The full event name would be
.Sy ereport.fs.zfs.\& Ns Em SUBCLASS ,
but only the last part is listed here.
.Pp
.Bl -tag -compact -width "vdev.bad_guid_sum"
.It Sy checksum
Issued when a checksum error has been detected.
.It Sy io
Issued when there is an I/O error in a vdev in the pool.
.It Sy data
Issued when there have been data errors in the pool.
.It Sy deadman
Issued when an I/O request is determined to be "hung", this can be caused
by lost completion events due to flaky hardware or drivers.
See
.Sy zfs_deadman_failmode
in
.Xr zfs 4
for additional information regarding "hung" I/O detection and configuration.
.It Sy delay
Issued when a completed I/O request exceeds the maximum allowed time
specified by the
.Sy zio_slow_io_ms
module parameter.
This can be an indicator of problems with the underlying storage device.
The number of delay events is ratelimited by the
.Sy zfs_slow_io_events_per_second
module parameter.
.It Sy dio_verify
Issued when there was a checksum verify error after a Direct I/O write has been
issued.
This event can only take place if the module parameter
.Sy zfs_vdev_direct_write_verify
is not set to zero.
See
.Xr zfs 4
for more details on the
.Sy zfs_vdev_direct_write_verify
module paramter.
.It Sy config
Issued every time a vdev change have been done to the pool.
.It Sy zpool
Issued when a pool cannot be imported.
.It Sy zpool.destroy
Issued when a pool is destroyed.
.It Sy zpool.export
Issued when a pool is exported.
.It Sy zpool.import
Issued when a pool is imported.
.It Sy zpool.reguid
Issued when a REGUID (new unique identifier for the pool have been regenerated)
have been detected.
.It Sy vdev.unknown
Issued when the vdev is unknown.
Such as trying to clear device errors on a vdev that have failed/been kicked
from the system/pool and is no longer available.
.It Sy vdev.open_failed
Issued when a vdev could not be opened (because it didn't exist for example).
.It Sy vdev.corrupt_data
Issued when corrupt data have been detected on a vdev.
.It Sy vdev.no_replicas
Issued when there are no more replicas to sustain the pool.
This would lead to the pool being
.Em DEGRADED .
.It Sy vdev.bad_guid_sum
Issued when a missing device in the pool have been detected.
.It Sy vdev.too_small
Issued when the system (kernel) have removed a device, and ZFS
notices that the device isn't there any more.
This is usually followed by a
.Sy probe_failure
event.
.It Sy vdev.bad_label
Issued when the label is OK but invalid.
.It Sy vdev.bad_ashift
Issued when the ashift alignment requirement has increased.
.It Sy vdev.remove
Issued when a vdev is detached from a mirror (or a spare detached from a
vdev where it have been used to replace a failed drive - only works if
the original drive have been re-added).
.It Sy vdev.clear
Issued when clearing device errors in a pool.
Such as running
.Nm zpool Cm clear
on a device in the pool.
.It Sy vdev.check
Issued when a check to see if a given vdev could be opened is started.
.It Sy vdev.spare
Issued when a spare have kicked in to replace a failed device.
.It Sy vdev.autoexpand
Issued when a vdev can be automatically expanded.
.It Sy io_failure
Issued when there is an I/O failure in a vdev in the pool.
.It Sy probe_failure
Issued when a probe fails on a vdev.
This would occur if a vdev
have been kicked from the system outside of ZFS (such as the kernel
have removed the device).
.It Sy log_replay
Issued when the intent log cannot be replayed.
The can occur in the case of a missing or damaged log device.
.It Sy resilver.start
Issued when a resilver is started.
.It Sy resilver.finish
Issued when the running resilver have finished.
.It Sy scrub.start
Issued when a scrub is started on a pool.
.It Sy scrub.finish
Issued when a pool has finished scrubbing.
.It Sy scrub.abort
Issued when a scrub is aborted on a pool.
.It Sy scrub.resume
Issued when a scrub is resumed on a pool.
.It Sy scrub.paused
Issued when a scrub is paused on a pool.
.It Sy bootfs.vdev.attach
.El
.
.Sh PAYLOADS
This is the payload (data, information) that accompanies an
event.
.Pp
For
.Xr zed 8 ,
these are set to uppercase and prefixed with
.Sy ZEVENT_ .
.Pp
.Bl -tag -compact -width "vdev_cksum_errors"
.It Sy pool
Pool name.
.It Sy pool_failmode
Failmode -
.Sy wait ,
.Sy continue ,
or
.Sy panic .
See the
.Sy failmode
property in
.Xr zpoolprops 7
for more information.
.It Sy pool_guid
The GUID of the pool.
.It Sy pool_context
The load state for the pool (0=none, 1=open, 2=import, 3=tryimport, 4=recover
5=error).
.It Sy vdev_guid
The GUID of the vdev in question (the vdev failing or operated upon with
.Nm zpool Cm clear ,
etc.).
.It Sy vdev_type
Type of vdev -
.Sy disk ,
.Sy file ,
.Sy mirror ,
etc.
See the
.Sy Virtual Devices
section of
.Xr zpoolconcepts 7
for more information on possible values.
.It Sy vdev_path
Full path of the vdev, including any
.Em -partX .
.It Sy vdev_devid
ID of vdev (if any).
.It Sy vdev_fru
Physical FRU location.
.It Sy vdev_state
State of vdev (0=uninitialized, 1=closed, 2=offline, 3=removed, 4=failed to
open, 5=faulted, 6=degraded, 7=healthy).
.It Sy vdev_ashift
The ashift value of the vdev.
.It Sy vdev_complete_ts
The time the last I/O request completed for the specified vdev.
.It Sy vdev_delta_ts
The time since the last I/O request completed for the specified vdev.
.It Sy vdev_spare_paths
List of spares, including full path and any
.Em -partX .
.It Sy vdev_spare_guids
GUID(s) of spares.
.It Sy vdev_read_errors
How many read errors that have been detected on the vdev.
.It Sy vdev_write_errors
How many write errors that have been detected on the vdev.
.It Sy vdev_cksum_errors
How many checksum errors that have been detected on the vdev.
.It Sy parent_guid
GUID of the vdev parent.
.It Sy parent_type
Type of parent.
See
.Sy vdev_type .
.It Sy parent_path
Path of the vdev parent (if any).
.It Sy parent_devid
ID of the vdev parent (if any).
.It Sy zio_objset
The object set number for a given I/O request.
.It Sy zio_object
The object number for a given I/O request.
.It Sy zio_level
The indirect level for the block.
Level 0 is the lowest level and includes data blocks.
Values > 0 indicate metadata blocks at the appropriate level.
.It Sy zio_blkid
The block ID for a given I/O request.
.It Sy zio_err
The error number for a failure when handling a given I/O request,
compatible with
.Xr errno 3
with the value of
.Sy EBADE
used to indicate a ZFS checksum error.
.It Sy zio_offset
The offset in bytes of where to write the I/O request for the specified vdev.
.It Sy zio_size
The size in bytes of the I/O request.
.It Sy zio_flags
The current flags describing how the I/O request should be handled.
See the
.Sy I/O FLAGS
section for the full list of I/O flags.
.It Sy zio_stage
The current stage of the I/O in the pipeline.
See the
.Sy I/O STAGES
section for a full list of all the I/O stages.
.It Sy zio_pipeline
The valid pipeline stages for the I/O.
See the
.Sy I/O STAGES
section for a full list of all the I/O stages.
.It Sy zio_delay
The time elapsed (in nanoseconds) waiting for the block layer to complete the
I/O request.
Unlike
.Sy zio_delta ,
this does not include any vdev queuing time and is
therefore solely a measure of the block layer performance.
.It Sy zio_timestamp
The time when a given I/O request was submitted.
.It Sy zio_delta
The time required to service a given I/O request.
.It Sy prev_state
The previous state of the vdev.
.It Sy cksum_algorithm
Checksum algorithm used.
See
.Xr zfsprops 7
for more information on the available checksum algorithms.
.It Sy cksum_byteswap
Whether or not the data is byteswapped.
.It Sy bad_ranges
.No [\& Ns Ar start , end )
pairs of corruption offsets.
Offsets are always aligned on a 64-bit boundary,
and can include some gaps of non-corruption.
(See
.Sy bad_ranges_min_gap )
.It Sy bad_ranges_min_gap
In order to bound the size of the
.Sy bad_ranges
array, gaps of non-corruption
less than or equal to
.Sy bad_ranges_min_gap
bytes have been merged with
adjacent corruption.
Always at least 8 bytes, since corruption is detected on a 64-bit word basis.
.It Sy bad_range_sets
This array has one element per range in
.Sy bad_ranges .
Each element contains
the count of bits in that range which were clear in the good data and set
in the bad data.
.It Sy bad_range_clears
This array has one element per range in
.Sy bad_ranges .
Each element contains
the count of bits for that range which were set in the good data and clear in
the bad data.
.It Sy bad_set_bits
If this field exists, it is an array of
.Pq Ar bad data No & ~( Ns Ar good data ) ;
that is, the bits set in the bad data which are cleared in the good data.
Each element corresponds a byte whose offset is in a range in
.Sy bad_ranges ,
and the array is ordered by offset.
Thus, the first element is the first byte in the first
.Sy bad_ranges
range, and the last element is the last byte in the last
.Sy bad_ranges
range.
.It Sy bad_cleared_bits
Like
.Sy bad_set_bits ,
but contains
.Pq Ar good data No & ~( Ns Ar bad data ) ;
that is, the bits set in the good data which are cleared in the bad data.
.El
.
.Sh I/O STAGES
The ZFS I/O pipeline is comprised of various stages which are defined below.
The individual stages are used to construct these basic I/O
operations: Read, Write, Free, Claim, Flush and Trim.
These stages may be
set on an event to describe the life cycle of a given I/O request.
.Pp
.TS
tab(:);
l l l .
Stage:Bit Mask:Operations
_:_:_
ZIO_STAGE_OPEN:0x00000001:RWFCXT
ZIO_STAGE_READ_BP_INIT:0x00000002:R-----
ZIO_STAGE_WRITE_BP_INIT:0x00000004:-W----
ZIO_STAGE_FREE_BP_INIT:0x00000008:--F---
ZIO_STAGE_ISSUE_ASYNC:0x00000010:-WF--T
ZIO_STAGE_WRITE_COMPRESS:0x00000020:-W----
ZIO_STAGE_ENCRYPT:0x00000040:-W----
ZIO_STAGE_CHECKSUM_GENERATE:0x00000080:-W----
ZIO_STAGE_NOP_WRITE:0x00000100:-W----
ZIO_STAGE_BRT_FREE:0x00000200:--F---
ZIO_STAGE_DDT_READ_START:0x00000400:R-----
ZIO_STAGE_DDT_READ_DONE:0x00000800:R-----
ZIO_STAGE_DDT_WRITE:0x00001000:-W----
ZIO_STAGE_DDT_FREE:0x00002000:--F---
ZIO_STAGE_GANG_ASSEMBLE:0x00004000:RWFC--
ZIO_STAGE_GANG_ISSUE:0x00008000:RWFC--
ZIO_STAGE_DVA_THROTTLE:0x00010000:-W----
ZIO_STAGE_DVA_ALLOCATE:0x00020000:-W----
ZIO_STAGE_DVA_FREE:0x00040000:--F---
ZIO_STAGE_DVA_CLAIM:0x00080000:---C--
ZIO_STAGE_READY:0x00100000:RWFCIT
ZIO_STAGE_VDEV_IO_START:0x00200000:RW--XT
ZIO_STAGE_VDEV_IO_DONE:0x00400000:RW--XT
ZIO_STAGE_VDEV_IO_ASSESS:0x00800000:RW--XT
ZIO_STAGE_CHECKSUM_VERIFY:0x01000000:R-----
ZIO_STAGE_DIO_CHECKSUM_VERIFY:0x02000000:-W----
ZIO_STAGE_DONE:0x04000000:RWFCXT
.TE
.
.Sh I/O FLAGS
Every I/O request in the pipeline contains a set of flags which describe its
function and are used to govern its behavior.
These flags will be set in an event as a
.Sy zio_flags
payload entry.
.Pp
.TS
tab(:);
l l .
Flag:Bit Mask
_:_
ZIO_FLAG_DONT_AGGREGATE:0x00000001
ZIO_FLAG_IO_REPAIR:0x00000002
ZIO_FLAG_SELF_HEAL:0x00000004
ZIO_FLAG_RESILVER:0x00000008
ZIO_FLAG_SCRUB:0x00000010
ZIO_FLAG_SCAN_THREAD:0x00000020
ZIO_FLAG_PHYSICAL:0x00000040
ZIO_FLAG_CANFAIL:0x00000080
ZIO_FLAG_SPECULATIVE:0x00000100
ZIO_FLAG_CONFIG_WRITER:0x00000200
ZIO_FLAG_DONT_RETRY:0x00000400
ZIO_FLAG_NODATA:0x00001000
ZIO_FLAG_INDUCE_DAMAGE:0x00002000
ZIO_FLAG_IO_ALLOCATING:0x00004000
ZIO_FLAG_IO_RETRY:0x00008000
ZIO_FLAG_PROBE:0x00010000
ZIO_FLAG_TRYHARD:0x00020000
ZIO_FLAG_OPTIONAL:0x00040000
ZIO_FLAG_DONT_QUEUE:0x00080000
ZIO_FLAG_DONT_PROPAGATE:0x00100000
ZIO_FLAG_IO_BYPASS:0x00200000
ZIO_FLAG_IO_REWRITE:0x00400000
ZIO_FLAG_RAW_COMPRESS:0x00800000
ZIO_FLAG_RAW_ENCRYPT:0x01000000
ZIO_FLAG_GANG_CHILD:0x02000000
ZIO_FLAG_DDT_CHILD:0x04000000
ZIO_FLAG_GODFATHER:0x08000000
ZIO_FLAG_NOPWRITE:0x10000000
ZIO_FLAG_REEXECUTED:0x20000000
ZIO_FLAG_DELEGATED:0x40000000
ZIO_FLAG_FASTWRITE:0x80000000
.TE
.
.Sh SEE ALSO
.Xr zfs 4 ,
.Xr zed 8 ,
.Xr zpool-wait 8
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