[Xen-users] RE: Tutorial : Debian, Xen and CLUSTER / GFS Support

[PAINCHAUD Christophe <cpainchaud@xxxxxxxxxxx>]

>Hey, nice tutorial :)
Thank you ;)

>Have you got domUs running with image-files on a gfs?

        I tried to put some domUs images on a GFS shared (through GNBD)
filesystem. Everything was running fine until I launched the domU : I had
tons of I/O errors. On CLUSTER ML, many users are reporting the same problem
when they are trying to lock and read/write on a very large file (over 1Gb).


        So I am using another way (which is in fact the ENBD way, shared
block devices over network). I created some LVM volumes VM01, VM02, VM03
(that I formatted with EXT3) then I exported them in GNBD. All my Xen nodes
are importing volumes from my GNBD1 server and I can run my domU very
smoothly. So far I was able to produce 55MBytes/s writes on the LVM volumes!
That's really a performant technology. I think I won't be able to do better
unless I use some fiber instead of my Gigabit interface (and I would run
into the SCSI speed limit of my disks :p). CPU on both machines was not much
used.

        The LVM solution is also interesting for backups : you can do a
snapshot of a volume and then make a backup of it, then destroy the
snapshot. It doesn't require to stop the VM using the volume.

        I will retry the domU image on GFS later, may be I did something
wrong. I would be glad to know if any of you got read of the read/write/lock
error when running a domU from it.


Christophe PAINCHAUD

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