tags 594069 + confirmed upstream
severity 594069 important
thanks
Ok. Indeed, qcow2 become MUCH slower in 0.12.5 compared with
0.12.4. This is due to a series of patches that went into 0.12.5
upstream to make qcow2 (and other similar formats) metadata
updates syncronous. Like this:
commit 37060c28e522843fbf6f7e59af745dfcb05b132c
Author: Kevin Wolf <kw...@redhat.com>
Date: Wed Jul 14 12:11:51 2010 +0200
qcow2: Use bdrv_(p)write_sync for metadata writes
Use bdrv_(p)write_sync to ensure metadata integrity in case of a crash.
Signed-off-by: Kevin Wolf <kw...@redhat.com>
(cherry picked from commit 8b3b720620a1137a1b794fc3ed64734236f94e06)
...
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -62,8 +62,8 @@ int qcow2_grow_l1_table(BlockDriverState *bs, int min_size)
- ret = bdrv_pwrite(s->hd, new_l1_table_offset, new_l1_table, new_l1_size2);
+ ret = bdrv_pwrite_sync(s->hd, new_l1_table_offset, new_l1_table,
new_l1_size2);
In other words, before that change, qcow2 format were unsafe
against host crashes, it were possible to get data corruptions.
Now that is fixed, but the cost is insanely slow operations.
I'll revert these patches for squeeze, restoring the previous
(unsafe) behavour: it is better to have something than not
have anything, because the resulting qcow2 is now completely
unusable.
Raising severity to important because this is really important
problem.
Thanks!
/mjt
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