24fe1bf621
and use it for plugin linked clone This also enable extended_l2=on, as it's mandatory for backing file preallocation. Preallocation was missing previously, so it should increase performance for linked clone now (around x5 in randwrite 4k) cluster_size is set to 128k, as it reduce qcow2 overhead (reduce disk, but also memory needed to cache metadatas) l2_extended is not enabled yet on base image, but it could help too to reduce overhead without impacting performance 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 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 Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>