3a20013fbb
When creating an image with preallocation "off" or "falloc", the first
block of the image is typically not allocated. When using Gluster
storage backed by XFS filesystem, reading this block using direct I/O
succeeds regardless of request length, fooling alignment detection.
In this case we fallback to a safe value (4096) instead of the optimal
value (512), which may lead to unneeded data copying when aligning
requests. Allocating the first block avoids the fallback.
Since we allocate the first block even with preallocation=off, we no
longer create images with zero disk size:
$ ./qemu-img create -f raw test.raw 1g
Formatting 'test.raw', fmt=raw size=1073741824
$ ls -lhs test.raw
4.0K -rw-r--r--. 1 nsoffer nsoffer 1.0G Aug 16 23:48 test.raw
And converting the image requires additional cluster:
$ ./qemu-img measure -f raw -O qcow2 test.raw
required size: 458752
fully allocated size: 1074135040
When using format like vmdk with multiple files per image, we allocate
one block per file:
$ ./qemu-img create -f vmdk -o subformat=twoGbMaxExtentFlat test.vmdk 4g
Formatting 'test.vmdk', fmt=vmdk size=4294967296 compat6=off hwversion=undefined subformat=twoGbMaxExtentFlat
$ ls -lhs test*.vmdk
4.0K -rw-r--r--. 1 nsoffer nsoffer 2.0G Aug 27 03:23 test-f001.vmdk
4.0K -rw-r--r--. 1 nsoffer nsoffer 2.0G Aug 27 03:23 test-f002.vmdk
4.0K -rw-r--r--. 1 nsoffer nsoffer 353 Aug 27 03:23 test.vmdk
I did quick performance test for copying disks with qemu-img convert to
new raw target image to Gluster storage with sector size of 512 bytes:
for i in $(seq 10); do
rm -f dst.raw
sleep 10
time ./qemu-img convert -f raw -O raw -t none -T none src.raw dst.raw
done
Here is a table comparing the total time spent:
Type Before(s) After(s) Diff(%)
---------------------------------------
real 530.028 469.123 -11.4
user 17.204 10.768 -37.4
sys 17.881 7.011 -60.7
We can see very clear improvement in CPU usage.
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Message-id: 20190827010528.8818-2-nsoffer@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
86 lines
2.4 KiB
Bash
Executable File
86 lines
2.4 KiB
Bash
Executable File
#!/usr/bin/env bash
|
|
#
|
|
# Test creating raw image preallocation mode
|
|
#
|
|
# Copyright (C) 2017 Nir Soffer <nirsof@gmail.com>
|
|
#
|
|
# This program is free software; you can redistribute it and/or modify
|
|
# it under the terms of the GNU General Public License as published by
|
|
# the Free Software Foundation; either version 2 of the License, or
|
|
# (at your option) any later version.
|
|
#
|
|
# This program is distributed in the hope that it will be useful,
|
|
# but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
# GNU General Public License for more details.
|
|
#
|
|
# You should have received a copy of the GNU General Public License
|
|
# along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
#
|
|
|
|
# creator
|
|
owner=nirsof@gmail.com
|
|
|
|
seq=`basename $0`
|
|
echo "QA output created by $seq"
|
|
|
|
status=1 # failure is the default!
|
|
|
|
_cleanup()
|
|
{
|
|
_cleanup_test_img
|
|
rm -f "$TEST_DIR/empty"
|
|
}
|
|
trap "_cleanup; exit \$status" 0 1 2 3 15
|
|
|
|
# Some file systems sometimes allocate extra blocks independently of
|
|
# the file size. This function hides the resulting difference in the
|
|
# stat -c '%b' output.
|
|
# Parameter 1: Number of blocks an empty file occupies
|
|
# Parameter 2: Minimal number of blocks in an image
|
|
# Parameter 3: Image size in bytes
|
|
_filter_blocks()
|
|
{
|
|
extra_blocks=$1
|
|
min_blocks=$2
|
|
img_size=$3
|
|
|
|
sed -e "s/blocks=$min_blocks\\(\$\\|[^0-9]\\)/min allocation/" \
|
|
-e "s/blocks=$((extra_blocks + img_size / 512))\\(\$\\|[^0-9]\\)/max allocation/"
|
|
}
|
|
|
|
# get standard environment, filters and checks
|
|
. ./common.rc
|
|
. ./common.filter
|
|
|
|
_supported_fmt raw
|
|
_supported_proto file
|
|
_supported_os Linux
|
|
|
|
size=$((1 * 1024 * 1024))
|
|
|
|
touch "$TEST_DIR/empty"
|
|
extra_blocks=$(stat -c '%b' "$TEST_DIR/empty")
|
|
|
|
# We always write the first byte; check how many blocks this filesystem
|
|
# allocates to match empty image alloation.
|
|
printf "\0" > "$TEST_DIR/empty"
|
|
min_blocks=$(stat -c '%b' "$TEST_DIR/empty")
|
|
|
|
echo
|
|
echo "== creating image with default preallocation =="
|
|
_make_test_img $size | _filter_imgfmt
|
|
stat -c "size=%s, blocks=%b" $TEST_IMG | _filter_blocks $extra_blocks $min_blocks $size
|
|
|
|
for mode in off full falloc; do
|
|
echo
|
|
echo "== creating image with preallocation $mode =="
|
|
IMGOPTS=preallocation=$mode _make_test_img $size | _filter_imgfmt
|
|
stat -c "size=%s, blocks=%b" $TEST_IMG | _filter_blocks $extra_blocks $min_blocks $size
|
|
done
|
|
|
|
# success, all done
|
|
echo "*** done"
|
|
rm -f $seq.full
|
|
status=0
|