Hi all,
I'm still trying to track down the cause of disk write slowness when
passing through disks to a DomU.
I've restructured things a little and now pass the raid array (/dev/md3)
directly to the DomU. When running a xfs_fsr on the filesystem from
within the Dom0, I get the following:
# iostat -m 5
(....)
avg-cpu: %user %nice %system %iowait %steal %idle
0.11 0.00 9.23 44.64 0.21 45.81
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdc 286.20 17.22 34.15 86 170
sdf 284.20 17.45 34.43 87 172
sdd 217.40 17.25 34.15 86 170
sde 211.00 17.25 34.38 86 171
md3 1095.40 69.20 67.18 346 335
This is with the RAID6 mounted on /mnt/fileshare from within the Dom0.
Speeds are about what I would expect for the task that is going on.
With no changes at all to the setup or the RAID, I attach the same RAID6
array to a DomU:
# xm block-attach zeus.vm phy:/dev/md3 xvdb w
Now run xfs_fsr from within the DomU, I look at the same output from
iostat on Dom0:
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 2.35 0.00 0.34 97.31
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdc 702.40 11.28 16.09 56 80
sdf 701.00 11.26 16.15 56 80
sdd 698.00 11.18 15.95 55 79
sde 700.60 11.27 16.19 56 80
md3 1641.00 30.30 29.87 151 149
I'm seeing this consistently across all methods of speed testing (dd,
bonnie++, etc).
If I remove and attach a single disk from the array and run tests on
that, I obtain full speed for the single drive. As soon as the array is
passed, the speed drops significantly (as seen above).
I have copied in the linux-raid list to this - as it seems to only
affect md arrays passed to the Xen DomU guests.
Where do we start debugging this?
--
Steven Haigh
Email: netwiz@xxxxxxxxx
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
