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[Qemu-devel] [Bug 1126369] Re: qemu-img snapshot -c is unreasonably slow
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [Bug 1126369] Re: qemu-img snapshot -c is unreasonably slow |
Date: |
Fri, 15 Feb 2013 19:55:45 -0000 |
Skipping the bdrv_flush() in update_cluster_refcount() gives a huge
speed-up from over 3 minutes down to <1 second. I think Kevin already
discovered this in the past.
Now we need to figure out how to safely perform the updates without
flushing after each L2 table refcount increment.
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https://bugs.launchpad.net/bugs/1126369
Title:
qemu-img snapshot -c is unreasonably slow
Status in QEMU:
New
Bug description:
Something fishy is going on with qcow2 internal snapshot creation
times. I don't know if this is a regression because I haven't used
internal snapshots in the past.
QEMU 1.4-rc2:
$ qemu-img create -f qcow2 test.qcow2 -o size=50G,preallocation=metadata
$ time qemu-img snapshot -c new test.qcow2
real 3m39.147s
user 0m10.748s
sys 0m26.165s
(This is on an SSD)
I expect snapshot creation to take under 1 second.
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