On 27.08.19 18:58, Max Reitz wrote: > On 27.08.19 03:05, Nir Soffer wrote: >> 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 <nsof...@redhat.com> >> --- >> block/file-posix.c | 51 +++++++++++++++++++ >> tests/qemu-iotests/059.out | 2 +- >> tests/qemu-iotests/{150.out => 150.out.qcow2} | 0 >> tests/qemu-iotests/150.out.raw | 12 +++++ >> tests/qemu-iotests/175 | 19 ++++--- >> tests/qemu-iotests/175.out | 8 +-- >> tests/qemu-iotests/178.out.qcow2 | 4 +- >> tests/qemu-iotests/221.out | 12 +++-- >> tests/qemu-iotests/253.out | 12 +++-- >> 9 files changed, 99 insertions(+), 21 deletions(-) >> rename tests/qemu-iotests/{150.out => 150.out.qcow2} (100%) >> create mode 100644 tests/qemu-iotests/150.out.raw > > Reviewed-by: Max Reitz <mre...@redhat.com> > > Maybe it’ll break the vmdk iotests when using a non-default subformat; > but currently running the iotests for non-default VMDK subformats is > broken anyway, so it doesn’t matter.
(Good news, 059 really was the only issue for VMDK.)
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