OpenZFS 9318 - vol_volsize_to_reservation does not account for raidz skip blocks

When a volume is created in a pool with raidz vdevs and
volblocksize != 128k, the volume can reference more space than is
reserved with the automatically calculated refreservation.  There
are two deficiencies in vol_volsize_to_reservation that contribute
to this:

  1) Skip blocks may be added to keep each allocation a multiple
     of parity + 1. This is the dominating factor when volblocksize
     is close to 2^ashift.

  2) raidz deflation for 128 KB blocks is different for most other
     block sizes.

See "The theory of raidz space accounting" comment in
libzfs_dataset.c for a full explanation.

Authored by: Mike Gerdts <mike.gerdts@joyent.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed by: Sanjay Nadkarni <sanjay.nadkarni@nexenta.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Kody Kantor <kody.kantor@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Dan McDonald <danmcd@joyent.com>
Ported-by: Mike Gerdts <mike.gerdts@joyent.com>

Porting Notes:
* ZTS: wait for zvols to exist before writing
* ZTS: use log_must_busy with {zpool|zfs} destroy

OpenZFS-issue: https://www.illumos.org/issues/9318
OpenZFS-commit: https://github.com/illumos/illumos-gate/commit/b73ccab0
Closes #8973
This commit is contained in:
Mike Gerdts 2019-06-30 23:38:07 +00:00 committed by Tony Hutter
parent 350646563f
commit f3f46b0e45
7 changed files with 520 additions and 14 deletions

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@ -29,6 +29,7 @@
* Copyright 2016 Nexenta Systems, Inc.
* Copyright (c) 2019 Datto Inc.
* Copyright (c) 2019, loli10K <ezomori.nozomu@gmail.com>
* Copyright 2019 Joyent, Inc.
*/
#include <assert.h>
@ -992,10 +993,11 @@ zfs_do_create(int argc, char **argv)
zpool_close(zpool_handle);
goto error;
}
zpool_close(zpool_handle);
volsize = zvol_volsize_to_reservation(volsize, real_props);
volsize = zvol_volsize_to_reservation(zpool_handle, volsize,
real_props);
nvlist_free(real_props);
zpool_close(zpool_handle);
if (nvlist_lookup_string(props, zfs_prop_to_name(resv_prop),
&strval) != 0) {

View File

@ -22,7 +22,7 @@
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2011, 2018 by Delphix. All rights reserved.
* Copyright (c) 2012, Joyent, Inc. All rights reserved.
* Copyright Joyent, Inc.
* Copyright (c) 2013 Steven Hartland. All rights reserved.
* Copyright (c) 2016, Intel Corporation.
* Copyright 2016 Nexenta Systems, Inc.
@ -687,7 +687,8 @@ extern int zfs_hold(zfs_handle_t *, const char *, const char *,
extern int zfs_hold_nvl(zfs_handle_t *, int, nvlist_t *);
extern int zfs_release(zfs_handle_t *, const char *, const char *, boolean_t);
extern int zfs_get_holds(zfs_handle_t *, nvlist_t **);
extern uint64_t zvol_volsize_to_reservation(uint64_t, nvlist_t *);
extern uint64_t zvol_volsize_to_reservation(zpool_handle_t *, uint64_t,
nvlist_t *);
typedef int (*zfs_userspace_cb_t)(void *arg, const char *domain,
uid_t rid, uint64_t space);

View File

@ -21,7 +21,7 @@
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2018, Joyent, Inc. All rights reserved.
* Copyright 2019 Joyent, Inc.
* Copyright (c) 2011, 2017 by Delphix. All rights reserved.
* Copyright (c) 2012 DEY Storage Systems, Inc. All rights reserved.
* Copyright (c) 2012 Pawel Jakub Dawidek <pawel@dawidek.net>.
@ -1618,6 +1618,7 @@ zfs_add_synthetic_resv(zfs_handle_t *zhp, nvlist_t *nvl)
uint64_t new_reservation;
zfs_prop_t resv_prop;
nvlist_t *props;
zpool_handle_t *zph = zpool_handle(zhp);
/*
* If this is an existing volume, and someone is setting the volsize,
@ -1632,7 +1633,7 @@ zfs_add_synthetic_resv(zfs_handle_t *zhp, nvlist_t *nvl)
fnvlist_add_uint64(props, zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE),
zfs_prop_get_int(zhp, ZFS_PROP_VOLBLOCKSIZE));
if ((zvol_volsize_to_reservation(old_volsize, props) !=
if ((zvol_volsize_to_reservation(zph, old_volsize, props) !=
old_reservation) || nvlist_exists(nvl,
zfs_prop_to_name(resv_prop))) {
fnvlist_free(props);
@ -1643,7 +1644,7 @@ zfs_add_synthetic_resv(zfs_handle_t *zhp, nvlist_t *nvl)
fnvlist_free(props);
return (-1);
}
new_reservation = zvol_volsize_to_reservation(new_volsize, props);
new_reservation = zvol_volsize_to_reservation(zph, new_volsize, props);
fnvlist_free(props);
if (nvlist_add_uint64(nvl, zfs_prop_to_name(resv_prop),
@ -1698,7 +1699,8 @@ zfs_fix_auto_resv(zfs_handle_t *zhp, nvlist_t *nvl)
volsize = zfs_prop_get_int(zhp, ZFS_PROP_VOLSIZE);
}
resvsize = zvol_volsize_to_reservation(volsize, props);
resvsize = zvol_volsize_to_reservation(zpool_handle(zhp), volsize,
props);
fnvlist_free(props);
(void) nvlist_remove_all(nvl, zfs_prop_to_name(prop));
@ -5363,12 +5365,176 @@ zfs_get_holds(zfs_handle_t *zhp, nvlist_t **nvl)
}
/*
* Convert the zvol's volume size to an appropriate reservation.
* The theory of raidz space accounting
*
* The "referenced" property of RAIDZ vdevs is scaled such that a 128KB block
* will "reference" 128KB, even though it allocates more than that, to store the
* parity information (and perhaps skip sectors). This concept of the
* "referenced" (and other DMU space accounting) being lower than the allocated
* space by a constant factor is called "raidz deflation."
*
* As mentioned above, the constant factor for raidz deflation assumes a 128KB
* block size. However, zvols typically have a much smaller block size (default
* 8KB). These smaller blocks may require proportionally much more parity
* information (and perhaps skip sectors). In this case, the change to the
* "referenced" property may be much more than the logical block size.
*
* Suppose a raidz vdev has 5 disks with ashift=12. A 128k block may be written
* as follows.
*
* +-------+-------+-------+-------+-------+
* | disk1 | disk2 | disk3 | disk4 | disk5 |
* +-------+-------+-------+-------+-------+
* | P0 | D0 | D8 | D16 | D24 |
* | P1 | D1 | D9 | D17 | D25 |
* | P2 | D2 | D10 | D18 | D26 |
* | P3 | D3 | D11 | D19 | D27 |
* | P4 | D4 | D12 | D20 | D28 |
* | P5 | D5 | D13 | D21 | D29 |
* | P6 | D6 | D14 | D22 | D30 |
* | P7 | D7 | D15 | D23 | D31 |
* +-------+-------+-------+-------+-------+
*
* Above, notice that 160k was allocated: 8 x 4k parity sectors + 32 x 4k data
* sectors. The dataset's referenced will increase by 128k and the pool's
* allocated and free properties will be adjusted by 160k.
*
* A 4k block written to the same raidz vdev will require two 4k sectors. The
* blank cells represent unallocated space.
*
* +-------+-------+-------+-------+-------+
* | disk1 | disk2 | disk3 | disk4 | disk5 |
* +-------+-------+-------+-------+-------+
* | P0 | D0 | | | |
* +-------+-------+-------+-------+-------+
*
* Above, notice that the 4k block required one sector for parity and another
* for data. vdev_raidz_asize() will return 8k and as such the pool's allocated
* and free properties will be adjusted by 8k. The dataset will not be charged
* 8k. Rather, it will be charged a value that is scaled according to the
* overhead of the 128k block on the same vdev. This 8k allocation will be
* charged 8k * 128k / 160k. 128k is from SPA_OLD_MAXBLOCKSIZE and 160k is as
* calculated in the 128k block example above.
*
* Every raidz allocation is sized to be a multiple of nparity+1 sectors. That
* is, every raidz1 allocation will be a multiple of 2 sectors, raidz2
* allocations are a multiple of 3 sectors, and raidz3 allocations are a
* multiple of of 4 sectors. When a block does not fill the required number of
* sectors, skip blocks (sectors) are used.
*
* An 8k block being written to a raidz vdev may be written as follows:
*
* +-------+-------+-------+-------+-------+
* | disk1 | disk2 | disk3 | disk4 | disk5 |
* +-------+-------+-------+-------+-------+
* | P0 | D0 | D1 | S0 | |
* +-------+-------+-------+-------+-------+
*
* In order to maintain the nparity+1 allocation size, a skip block (S0) was
* added. For this 8k block, the pool's allocated and free properties are
* adjusted by 16k and the dataset's referenced is increased by 16k * 128k /
* 160k. Again, 128k is from SPA_OLD_MAXBLOCKSIZE and 160k is as calculated in
* the 128k block example above.
*
* Compression may lead to a variety of block sizes being written for the same
* volume or file. There is no clear way to reserve just the amount of space
* that will be required, so the worst case (no compression) is assumed.
* Note that metadata blocks will typically be compressed, so the reservation
* size returned by zvol_volsize_to_reservation() will generally be slightly
* larger than the maximum that the volume can reference.
*/
/*
* Derived from function of same name in module/zfs/vdev_raidz.c. Returns the
* amount of space (in bytes) that will be allocated for the specified block
* size. Note that the "referenced" space accounted will be less than this, but
* not necessarily equal to "blksize", due to RAIDZ deflation.
*/
static uint64_t
vdev_raidz_asize(uint64_t ndisks, uint64_t nparity, uint64_t ashift,
uint64_t blksize)
{
uint64_t asize, ndata;
ASSERT3U(ndisks, >, nparity);
ndata = ndisks - nparity;
asize = ((blksize - 1) >> ashift) + 1;
asize += nparity * ((asize + ndata - 1) / ndata);
asize = roundup(asize, nparity + 1) << ashift;
return (asize);
}
/*
* Determine how much space will be allocated if it lands on the most space-
* inefficient top-level vdev. Returns the size in bytes required to store one
* copy of the volume data. See theory comment above.
*/
static uint64_t
volsize_from_vdevs(zpool_handle_t *zhp, uint64_t nblocks, uint64_t blksize)
{
nvlist_t *config, *tree, **vdevs;
uint_t nvdevs, v;
uint64_t ret = 0;
config = zpool_get_config(zhp, NULL);
if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &tree) != 0 ||
nvlist_lookup_nvlist_array(tree, ZPOOL_CONFIG_CHILDREN,
&vdevs, &nvdevs) != 0) {
return (nblocks * blksize);
}
for (v = 0; v < nvdevs; v++) {
char *type;
uint64_t nparity, ashift, asize, tsize;
nvlist_t **disks;
uint_t ndisks;
uint64_t volsize;
if (nvlist_lookup_string(vdevs[v], ZPOOL_CONFIG_TYPE,
&type) != 0 || strcmp(type, VDEV_TYPE_RAIDZ) != 0 ||
nvlist_lookup_uint64(vdevs[v], ZPOOL_CONFIG_NPARITY,
&nparity) != 0 ||
nvlist_lookup_uint64(vdevs[v], ZPOOL_CONFIG_ASHIFT,
&ashift) != 0 ||
nvlist_lookup_nvlist_array(vdevs[v], ZPOOL_CONFIG_CHILDREN,
&disks, &ndisks) != 0) {
continue;
}
/* allocation size for the "typical" 128k block */
tsize = vdev_raidz_asize(ndisks, nparity, ashift,
SPA_OLD_MAXBLOCKSIZE);
/* allocation size for the blksize block */
asize = vdev_raidz_asize(ndisks, nparity, ashift, blksize);
/*
* Scale this size down as a ratio of 128k / tsize. See theory
* statement above.
*/
volsize = nblocks * asize * SPA_OLD_MAXBLOCKSIZE / tsize;
if (volsize > ret) {
ret = volsize;
}
}
if (ret == 0) {
ret = nblocks * blksize;
}
return (ret);
}
/*
* Convert the zvol's volume size to an appropriate reservation. See theory
* comment above.
*
* Note: If this routine is updated, it is necessary to update the ZFS test
* suite's shell version in reservation.kshlib.
* suite's shell version in reservation.shlib.
*/
uint64_t
zvol_volsize_to_reservation(uint64_t volsize, nvlist_t *props)
zvol_volsize_to_reservation(zpool_handle_t *zph, uint64_t volsize,
nvlist_t *props)
{
uint64_t numdb;
uint64_t nblocks, volblocksize;
@ -5384,7 +5550,14 @@ zvol_volsize_to_reservation(uint64_t volsize, nvlist_t *props)
zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE),
&volblocksize) != 0)
volblocksize = ZVOL_DEFAULT_BLOCKSIZE;
nblocks = volsize/volblocksize;
nblocks = volsize / volblocksize;
/*
* Metadata defaults to using 128k blocks, not volblocksize blocks. For
* this reason, only the data blocks are scaled based on vdev config.
*/
volsize = volsize_from_vdevs(zph, nblocks, volblocksize);
/* start with metadnode L0-L6 */
numdb = 7;
/* calculate number of indirects */

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@ -755,7 +755,8 @@ tags = ['functional', 'refquota']
[tests/functional/refreserv]
tests = ['refreserv_001_pos', 'refreserv_002_pos', 'refreserv_003_pos',
'refreserv_004_pos', 'refreserv_005_pos']
'refreserv_004_pos', 'refreserv_005_pos', 'refreserv_multi_raidz',
'refreserv_raidz']
tags = ['functional', 'refreserv']
[tests/functional/removal]

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@ -6,7 +6,9 @@ dist_pkgdata_SCRIPTS = \
refreserv_002_pos.ksh \
refreserv_003_pos.ksh \
refreserv_004_pos.ksh \
refreserv_005_pos.ksh
refreserv_005_pos.ksh \
refreserv_multi_raidz.ksh \
refreserv_raidz.ksh
dist_pkgdata_DATA = \
refreserv.cfg

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@ -0,0 +1,197 @@
#!/bin/ksh -p
#
# This file and its contents are supplied under the terms of the
# Common Development and Distribution License ("CDDL"), version 1.0.
# You may only use this file in accordance with the terms of version
# 1.0 of the CDDL.
#
# A full copy of the text of the CDDL should have accompanied this
# source. A copy of the CDDL is also available via the Internet at
# http://www.illumos.org/license/CDDL.
#
#
# Copyright 2019 Joyent, Inc.
#
. $STF_SUITE/include/libtest.shlib
. $STF_SUITE/tests/functional/refreserv/refreserv.cfg
#
# DESCRIPTION:
# raidz refreservation=auto picks worst raidz vdev
#
# STRATEGY:
# 1. Create a pool with a single raidz vdev
# 2. For each block size [512b, 1k, 128k] or [4k, 8k, 128k]
# - create a volume
# - remember its refreservation
# - destroy the volume
# 3. Destroy the pool
# 4. Recreate the pool with one more disk in the vdev, then repeat steps
# 2 and 3.
#
# NOTES:
# 1. This test will use up to 14 disks but can cover the key concepts with
# 5 disks.
# 2. If the disks are a mixture of 4Kn and 512n/512e, failures are likely.
#
verify_runnable "global"
typeset -a alldisks=($DISKS)
# The larger the volsize, the better zvol_volsize_to_reservation() is at
# guessing the right number - though it is horrible with tiny blocks. At 10M on
# ashift=12, the estimate may be over 26% too high.
volsize=100
function cleanup
{
default_cleanup_noexit
default_setup_noexit "${alldisks[0]}"
}
log_assert "raidz refreservation=auto picks worst raidz vdev"
log_onexit cleanup
poolexists "$TESTPOOL" && log_must_busy zpool destroy "$TESTPOOL"
# Testing tiny block sizes on ashift=12 pools causes so much size inflation
# that small test disks may fill before creating small volumes. However,
# testing 512b and 1K blocks on ashift=9 pools is an ok approximation for
# testing the problems that arise from 4K and 8K blocks on ashift=12 pools.
bps=$(lsblk -nrdo min-io /dev/${alldisks[0]})
case "$bps" in
512)
allshifts=(9 10 17)
;;
4096)
allshifts=(12 13 17)
;;
*)
log_fail "bytes/sector: $bps != (512|4096)"
;;
esac
log_note "Testing in ashift=${allshifts[0]} mode"
typeset -A sizes=
#
# Determine the refreservation for a $volsize MiB volume on each raidz type at
# various block sizes.
#
for parity in 1 2 3; do
raid=raidz$parity
typeset -A sizes["$raid"]
# Ensure we hit scenarios with and without skip blocks
for ndisks in $((parity * 2)) $((parity * 2 + 1)); do
typeset -a disks=(${alldisks[0..$((ndisks - 1))]})
if (( ${#disks[@]} < ndisks )); then
log_note "Too few disks to test $raid-$ndisks"
continue
fi
typeset -A sizes["$raid"]["$ndisks"]
log_must zpool create "$TESTPOOL" "$raid" "${disks[@]}"
for bits in "${allshifts[@]}"; do
vbs=$((1 << bits))
log_note "Gathering refreservation for $raid-$ndisks" \
"volblocksize=$vbs"
vol=$TESTPOOL/$TESTVOL
log_must zfs create -V ${volsize}m \
-o volblocksize=$vbs "$vol"
refres=$(zfs get -Hpo value refreservation "$vol")
log_must test -n "$refres"
sizes["$raid"]["$ndisks"]["$vbs"]=$refres
log_must_busy zfs destroy "$vol"
done
log_must_busy zpool destroy "$TESTPOOL"
done
done
# A little extra info is always helpful when diagnosing problems. To
# pretty-print what you find in the log, do this in ksh:
# typeset -A sizes=(...)
# print -v sizes
log_note "sizes=$(print -C sizes)"
#
# Helper furnction for checking that refreservation is calculated properly in
# multi-vdev pools. "Properly" is defined as assuming that all vdevs are as
# space inefficient as the worst one.
#
function check_vdevs {
typeset raid=$1
typeset nd1=$2
typeset nd2=$3
typeset -a disks1 disks2
typeset vbs vol refres refres1 refres2 expect
disks1=(${alldisks[0..$((nd1 - 1))]})
disks2=(${alldisks[$nd1..$((nd1 + nd2 - 1))]})
if (( ${#disks2[@]} < nd2 )); then
log_note "Too few disks to test $raid-$nd1 + $raid=$nd2"
return
fi
log_must zpool create -f "$TESTPOOL" \
"$raid" "${disks1[@]}" "$raid" "${disks2[@]}"
for bits in "${allshifts[@]}"; do
vbs=$((1 << bits))
log_note "Verifying $raid-$nd1 $raid-$nd2 volblocksize=$vbs"
vol=$TESTPOOL/$TESTVOL
log_must zfs create -V ${volsize}m -o volblocksize=$vbs "$vol"
refres=$(zfs get -Hpo value refreservation "$vol")
log_must test -n "$refres"
refres1=${sizes["$raid"]["$nd1"]["$vbs"]}
refres2=${sizes["$raid"]["$nd2"]["$vbs"]}
if (( refres1 > refres2 )); then
log_note "Expecting refres ($refres) to match refres" \
"from $raid-$nd1 ($refres1)"
log_must test "$refres" -eq "$refres1"
else
log_note "Expecting refres ($refres) to match refres" \
"from $raid-$nd1 ($refres2)"
log_must test "$refres" -eq "$refres2"
fi
log_must zfs destroy "$vol"
done
log_must zpool destroy "$TESTPOOL"
}
#
# Verify that multi-vdev pools use the last optimistic size for all the
# permutations within a particular raidz variant.
#
for raid in "${!sizes[@]}"; do
# ksh likes to create a [0] item for us. Thanks, ksh!
[[ $raid == "0" ]] && continue
for nd1 in "${!sizes["$raid"][@]}"; do
# And with an empty array we get one key, ''. Thanks, ksh!
[[ $nd1 == "0" || -z "$nd1" ]] && continue
for nd2 in "${!sizes["$raid"][@]}"; do
[[ $nd2 == "0" || -z "$nd2" ]] && continue
check_vdevs "$raid" "$nd1" "$nd2"
done
done
done
log_pass "raidz refreservation=auto picks worst raidz vdev"

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@ -0,0 +1,130 @@
#!/bin/ksh -p
#
# This file and its contents are supplied under the terms of the
# Common Development and Distribution License ("CDDL"), version 1.0.
# You may only use this file in accordance with the terms of version
# 1.0 of the CDDL.
#
# A full copy of the text of the CDDL should have accompanied this
# source. A copy of the CDDL is also available via the Internet at
# http://www.illumos.org/license/CDDL.
#
#
# Copyright 2019 Joyent, Inc.
#
. $STF_SUITE/include/libtest.shlib
. $STF_SUITE/tests/functional/refreserv/refreserv.cfg
#
# DESCRIPTION:
# raidz refreservation=auto accounts for extra parity and skip blocks
#
# STRATEGY:
# 1. Create a pool with a single raidz vdev
# 2. For each block size [512b, 1k, 128k] or [4k, 8k, 128k]
# - create a volume
# - fully overwrite it
# - verify that referenced is less than or equal to reservation
# - destroy the volume
# 3. Destroy the pool
# 4. Recreate the pool with one more disk in the vdev, then repeat steps
# 2 and 3.
# 5. Repeat all steps above for raidz2 and raidz3.
#
# NOTES:
# 1. This test will use up to 14 disks but can cover the key concepts with
# 5 disks.
# 2. If the disks are a mixture of 4Kn and 512n/512e, failures are likely.
#
verify_runnable "global"
typeset -a alldisks=($DISKS)
# The larger the volsize, the better zvol_volsize_to_reservation() is at
# guessing the right number. At 10M on ashift=12, the estimate may be over 26%
# too high.
volsize=100
function cleanup
{
default_cleanup_noexit
default_setup_noexit "${alldisks[0]}"
}
log_assert "raidz refreservation=auto accounts for extra parity and skip blocks"
log_onexit cleanup
poolexists "$TESTPOOL" && log_must_busy zpool destroy "$TESTPOOL"
# Testing tiny block sizes on ashift=12 pools causes so much size inflation
# that small test disks may fill before creating small volumes. However,
# testing 512b and 1K blocks on ashift=9 pools is an ok approximation for
# testing the problems that arise from 4K and 8K blocks on ashift=12 pools.
bps=$(lsblk -nrdo min-io /dev/${alldisks[0]})
log_must test "$bps" -eq 512 -o "$bps" -eq 4096
case "$bps" in
512)
allshifts=(9 10 17)
maxpct=151
;;
4096)
allshifts=(12 13 17)
maxpct=110
;;
*)
log_fail "bytes/sector: $bps != (512|4096)"
;;
esac
log_note "Testing in ashift=${allshifts[0]} mode"
# This loop handles all iterations of steps 1 through 4 described in strategy
# comment above,
for parity in 1 2 3; do
raid=raidz$parity
# Ensure we hit scenarios with and without skip blocks
for ndisks in $((parity * 2)) $((parity * 2 + 1)); do
typeset -a disks=(${alldisks[0..$((ndisks - 1))]})
if (( ${#disks[@]} < ndisks )); then
log_note "Too few disks to test $raid-$ndisks"
continue
fi
log_must zpool create "$TESTPOOL" "$raid" "${disks[@]}"
for bits in "${allshifts[@]}"; do
vbs=$((1 << bits))
log_note "Testing $raid-$ndisks volblocksize=$vbs"
vol=$TESTPOOL/$TESTVOL
log_must zfs create -V ${volsize}m \
-o volblocksize=$vbs "$vol"
block_device_wait "/dev/zvol/$vol"
log_must dd if=/dev/zero of=/dev/zvol/$vol \
bs=1024k count=$volsize
sync
ref=$(zfs get -Hpo value referenced "$vol")
refres=$(zfs get -Hpo value refreservation "$vol")
log_must test -n "$ref"
log_must test -n "$refres"
typeset -F2 deltapct=$((refres * 100.0 / ref))
log_note "$raid-$ndisks refreservation $refres" \
"is $deltapct% of reservation $res"
log_must test "$ref" -le "$refres"
log_must test "$deltapct" -le $maxpct
log_must_busy zfs destroy "$vol"
done
log_must_busy zpool destroy "$TESTPOOL"
done
done
log_pass "raidz refreservation=auto accounts for extra parity and skip blocks"