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This is part of my work on qcow2 external snapshot, but could improve current
qcow2 linked clone
This patch serie move qemu_img_create to common helpers,
and enable preallocation on backed_image to increase performance
This require l2_extended=on on the backed image
I have done some benchmarks on localssd with 100gb qcow2, the performance in
randwrite 4k is 5x faster
some presentation of l2_extended=on are available here
https://www.youtube.com/watch?v=zJetcfDVFNw
https://www.youtube.com/watch?v=NfgLCdtkRus
I don't have enabled it for base image, as I think that Fabian see performance
regression some month ago.
but I don't see performance difference in my bench. (can you could test on your
side again ?)
It could help to reduce qcow2 overhead on disk,
and allow to keep more metadatas in memory for bigger image, as qemu default
memory l2_cache_size=1MB)
https://www.ibm.com/products/tutorials/how-to-tune-qemu-l2-cache-size-and-qcow2-cluster-size
Maybe more test with bigger image (>1TB) could be done too to see if it's help
bench on 100G qcow2 file:
fio --filename=/dev/sdb --direct=1 --rw=randwrite --bs=4k --iodepth=32
--ioengine=libaio --name=test
fio --filename=/dev/sdb --direct=1 --rw=randread --bs=4k --iodepth=32
--ioengine=libaio --name=test
base image:
randwrite 4k: prealloc=metadata, l2_extended=off, cluster_size=64k: 20215
randread 4k: prealloc=metadata, l2_extended=off, cluster_size=64k: 22219
randwrite 4k: prealloc=metadata, l2_extended=on, cluster_size=64k: 20217
randread 4k: prealloc=metadata, l2_extended=on, cluster_size=64k: 21742
randwrite 4k: prealloc=metadata, l2_extended=on, cluster_size=128k: 21599
randread 4k: prealloc=metadata, l2_extended=on, cluster_size=128k: 22037
linked clone image with backing file:
randwrite 4k: prealloc=metadata, l2_extended=off, cluster_size=64k: 3912
randread 4k: prealloc=metadata, l2_extended=off, cluster_size=64k: 21476
randwrite 4k: prealloc=metadata, l2_extended=on, cluster_size=64k: 20563
randread 4k: prealloc=metadata, l2_extended=on, cluster_size=64k: 22265
randwrite 4k: prealloc=metadata, l2_extended=on, cluster_size=128k: 18016
randread 4k: prealloc=metadata, l2_extended=on, cluster_size=128k: 21611
Alexandre Derumier (2):
common: add qemu_img_create an preallocation_cmd_option
common: qemu_img_create: add backing_file support
src/PVE/Storage/Common.pm | 62 ++++++++++++++++++++++++++++++
src/PVE/Storage/GlusterfsPlugin.pm | 2 +-
src/PVE/Storage/Plugin.pm | 52 +------------------------
3 files changed, 65 insertions(+), 51 deletions(-)
--
2.39.5
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