Dear Mantainer,
El 31/05/2014 03:41, Michael Tokarev escribió:
Control: tag -1 + moreinfo
31.05.2014 02:23, Ernesto wrote:
Package: qemu-utils
Version: 2.0.0+dfsg-4+b1
Severity: normal
Dear Maintainer,
I use qemu-nbd to mount a ext4 filesystem from a virtual disk image
which is stored in an NTFS partition. I have more space in the NTFS
partition than in my native-linux ones, but I need ext4, so this is a
good solution.
I use the virtual disk to compile source code, which grows up to 8-9
GB. I mount it with:
modprobe nbd && qemu-nbd -c /dev/nbd0 /path_to_image/trunk.qcow2 &&
mount /dev/nbd0 /path_to_mountpoint/mnt/
I used to have this setup on a Wheezy system, and its performance was
very good. Now, I upgraded to Jessie, and the same setup performs
poorly. I ran iozone disk benchmark on both systems, several times,
over the ext4 filesystem in the virtual disk:
If, when running the same kernel, by changing qemu-nbd you can
reproduce
the slowdown, in both cases, it will mean it's something in qemu-nbd.
If speed drops when you change kernel, it must be kernel.
I have Debian Jessie and I'm using for metrics the compilation of some
software. I did it several times, and it takes around:
1. in a ext4 filesystem:
real 34m5.764s
user 93m7.820s
sys 6m27.512s
2. ext4 on top of ntfs using qemu-utils 2.1+dfsg-4_amd64 (the version
that comes with Jessie)
real 69m49.165s
user 88m51.120s
sys 9m6.936s
3. ext4 on top of ntfs using qemu-utils, 1.1.2+dfsg-6a+deb7u3 (the
version that comes with Wheezy)
real 39m41.343s
user 91m30.928s
sys 8m49.000s
I repeated several times each run, the results being about the same.
Also tried to keep everything else the same. I ran the compilations from
the text console, in order to have the graphical interface out of the
picture. The difference is very significant.
Based on Michael's advise, I would say there is some kind of regression
on qemu-utils, I mean, under certain conditions the new version performs
worst than the old version.
I'd like to bring focus to the great performance of the old version. For
me, it makes using ext4 over ntfs feels almost like using ext4. Wouldn't
it be good to have that performance also on newer implementations?
Regards.
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