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bfe8043e92
Lazy refcounts is a performance optimization for qcow2 that postpones refcount metadata updates and instead marks the image dirty. In the case of crash or power failure the image will be left in a dirty state and repaired next time it is opened. Reducing metadata I/O is important for cache=writethrough and cache=directsync because these modes guarantee that data is on disk after each write (hence we cannot take advantage of caching updates in RAM). Refcount metadata is not needed for guest->file block address translation and therefore does not need to be on-disk at the time of write completion - this is the motivation behind the lazy refcount optimization. The lazy refcount optimization must be enabled at image creation time: qemu-img create -f qcow2 -o compat=1.1,lazy_refcounts=on a.qcow2 10G qemu-system-x86_64 -drive if=virtio,file=a.qcow2,cache=writethrough Update qemu-iotests 031 and 036 since the extension header size changes when we add feature bit table entries. Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
53 lines
1.4 KiB
Plaintext
53 lines
1.4 KiB
Plaintext
QA output created by 036
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=== Create image with unknown autoclear feature bit ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
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magic 0x514649fb
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version 3
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backing_file_offset 0x0
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backing_file_size 0x0
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cluster_bits 16
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size 67108864
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crypt_method 0
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l1_size 1
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l1_table_offset 0x30000
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refcount_table_offset 0x10000
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refcount_table_clusters 1
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nb_snapshots 0
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snapshot_offset 0x0
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incompatible_features 0x0
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compatible_features 0x0
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autoclear_features 0x8000000000000000
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refcount_order 4
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header_length 104
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=== Repair image ===
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No errors were found on the image.
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magic 0x514649fb
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version 3
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backing_file_offset 0x0
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backing_file_size 0x0
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cluster_bits 16
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size 67108864
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crypt_method 0
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l1_size 1
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l1_table_offset 0x30000
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refcount_table_offset 0x10000
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refcount_table_clusters 1
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nb_snapshots 0
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snapshot_offset 0x0
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incompatible_features 0x0
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compatible_features 0x0
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autoclear_features 0x0
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refcount_order 4
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header_length 104
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Header extension:
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magic 0x6803f857
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length 96
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data <binary>
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*** done
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