Re: [Xen-users] Block IO Questions

[Omar Siam <simar@xxxxxxx>]

Hi!
I have to say I've got similar strange behavior since I upgraded my home
grown storage server (Intel DQ35JO, disks attached to Q35, Core2 E6550,
40+ Mbps write) with brand new hardware (ASUS P8H77M-Pro, disks attached
to H77, Pentium G840, ok not that brand new). I didn't get much more
than your 10 Mbps.
System is a 3.2(.15) based Debian squeeze+backports for Dom0 and 3.2
based Debian testing+sid for DomU.

I improved the situation somwhat by setting xen-blkback's reqs parameter
to 512 (default is 64 but I don't fully understand what this actually
sets. There is a tempting comment in xen-blkback.c ;-) ).

I still don't get more then 40-50 Mbps in a linux PV vm (bonnie++, xfs)
the same Filesystem on md RAID5+lvm does 150 Mbps write 300 Mbps read
mounted in Dom0.

By the way I can't find any means by which a Dom0 can inform a vm of a
physical block size other than 512 (like 4k for example), but perhaps
that's irrelevant here.

Best regards
Omar Siam


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