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[Qemu-devel] [Bug 1422307] Re: qemu-nbd corrupts files
From: |
Pierre Schweitzer |
Subject: |
[Qemu-devel] [Bug 1422307] Re: qemu-nbd corrupts files |
Date: |
Wed, 18 Feb 2015 09:11:57 -0000 |
So, if I understand well, it's "just" some kind of race condition in the
handling of writes in the VDI driver of Qemu?
Does that mean it can also affect VMs running with VDI disk(s)?
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https://bugs.launchpad.net/bugs/1422307
Title:
qemu-nbd corrupts files
Status in QEMU:
New
Bug description:
Dear all,
On Trusty, in certain situations, try to copy files over a qemu-nbd
mounted file system leads to write errors (and thus, file corruption).
Here is the last example I tried:
-> virtual disk is a VDI disk
-> It has only one partition, in FAT
Here is my mount process:
# modprobe nbd max_part=63
# qemu-nbd -c /dev/nbd0 "virtual_disk.vdi"
# partprobe /dev/nbd0
# mount /dev/nbd0p1 /tmp/mnt/
Partition is properly mounted at that point:
/dev/nbd0p1 on /tmp/mnt type vfat (rw)
Now, when I copy a file (rather big, ~28MB):
# cp file_to_copy /tmp/mnt/ ; sync
# md5sum /tmp/mnt/file_to_copy
2efc9f32e4267782b11d63d2f128a363 /tmp/mnt/file_to_copy
# umount /tmp/mnt
# mount /dev/nbd0p1 /tmp/mnt/
# md5sum /tmp/mnt/file_to_copy
42b0a3bf73f704d03ce301716d7654de /tmp/mnt/file_to_copy
The first hash was obviously the right one.
On a previous attempt I did, I spotted thanks to vbindiff that parts of the
file were just filed with 0s instead of actual data.
It will randomly work after several attempts to write.
Version information:
# qemu-nbd --version
qemu-nbd version 0.0.1
Written by Anthony Liguori.
Cheers,
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