xen discuss - Jun 2008 - Xen save/restore HDD-performance

Hi,

i tried so save/restore a DomU running on xen-3.2-testing@fedora, but
i got only a restore speed 22MB/sec - therefore, a saved solaris-snv90-DomU
takes about 768MB/22 = 34 seconds to restore. This is independant of the
real diskperformance (tested with bonnie - about 60-130MB/sec - depends on test)

Is this a linux-xen-Dom0-topic or 
a general xen-topic (also happens in a solaris Dom0 ?)

I have no solaris Dom0  - so could somebody please 
try to save/restore any DomU running on solaris-Dom0 and tell me the speed of
restoring ?

Thx
Danny
 
 
This message posted from opensolaris.org

> i tried so save/restore a DomU running on xen-3.2-testing@fedora, but
> i got only a restore speed 22MB/sec - therefore, a saved solaris-snv90-DomU
> takes about 768MB/22 = 34 seconds to restore. This is independant of the
> real diskperformance (tested with bonnie - about 60-130MB/sec - depends on
test)
> 
> Is this a linux-xen-Dom0-topic or a general xen-topic (also happens in a
solaris Dom0?)
> 
> I have no solaris Dom0  - so could somebody please try to save/restore any
DomU running
> on solaris-Dom0 and tell me the speed of restoring ?
IIRC,the linux dom0 blkback driver bypasses the kernel''s buffer cache.
The solaris dom0 blkback driver is using the kernel''s buffer cache.


I just tried to save / restore an snv_89 pv domU on snv_93 (all 64-bit),
with the save file on an UFS filesystem:

# ptime xm save solaris /var/tmp/solaris.save

real       13.316
user        0.065
sys         0.040
# ptime xm restore /var/tmp/solaris.save

real        2.390
user        0.068
sys         0.037



The second save was slower, but it restored very fast:

# ptime xm save solaris /var/tmp/solaris.save

real       34.133
user        0.067
sys         0.038
# ptime xm restore /var/tmp/solaris.save

real        2.396
user        0.068
sys         0.037



Using a zfs filesystem for the save file was faster during
save;  here I also unmounted / remounted the zfs filesystem
to clear any cached bits from memory:

#  ptime xm save solaris /files2/test/solaris.save

real        7.735
user        0.069
sys         0.039

# zfs umount files2/test
# zfs mount files2/test
# ptime xm restore /files2/test/solaris.save

real        7.241
user        0.068
sys         0.037
 
 
This message posted from opensolaris.org

Hi Jürgen,

how much RAM did you "insert" in your DomU ? How big was the image
greated by xm restore ?

regards
Danny
 
 
This message posted from opensolaris.org
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> how much RAM did you "insert" in your DomU ? How big
> was the image greated by xm restore ?
I changed it from 512 mbytes to 768 mbytes, so that the
results should be comparable with your test

# ls -hl /files2/test/solaris.save
-rwxr-xr-x   1 xvm      xvm         770M Jun 23 18:42 /files2/test/solaris.save
 
 
This message posted from opensolaris.org

Thx very much - maybe i have to change from linux-Dom0 to solaris Dom0 (-:
First - i will ask the linux-xen mailinglist again for "fixing" this
....

Thx
Danny
 
 
This message posted from opensolaris.org