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Re: [Xen-users] XCP Storage

On Thu, Oct 27, 2011 at 12:47 AM, Denis Cardon <denis.cardon@xxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi Grant,

  > You will want to analyze your disk and network layout for the
 Âmachine and hosts though. All of the standard hardware performace
  >data applies to an iSCSI target ie. number of disks, RAID levels
 Âetc... It would be ideal for your XCP hosts to have dual network
  >cards so that networking data is sent across different
 Âcables/switches then the SAN data.

 ÂI agree, no matter how you access the storage, the load generated by
 Âthe applications needs to be supported by the speed and number of
 Âdisks, and RAID level. We've gone through the pain of having issues
 Âwith storage that seemed like they could be the iSCSI initiator, the
 ÂSAN network or buffers on the iSCSI storage device.... when it
 Âturned out, we were simply overloading the IO capabilities of the disks.

 ÂAlso, it seems I am reading that you can enable live migration on an
 ÂXCP pool without an external storage device at all, using local
 Âstorage in each host. Is that right?

 ÂHow does that work?

 ÂMy understand of shared storage is that one copy of the VM exists in
 Âa place accessible to the two hosts, so to do live migration the VM
 Âstorage doesn't actually move.

 ÂCan someone point me to some documentation that explains how
 ÂXenServer and XCP handle storage? It seems to be quite different
 Âthan VMware.


 ÂBrett Westover

I don't think it's that different. If you want to do migration your
storage needs to be remote. Currently XCP seems to support two types of
remote storage that can support migration - NFS and iSCSI software target.

I'd rather say that XCP needs "shared" storage rather than "remote" storage.

When creating a iscsi SR, xapi does automagically all the stuff behind the scene, setting the underlying PBD and the SR of type "shared". However you can also manually create the PBD on whatever /dev/ (which ought to be shared, be it iscsi/aoe/drbd...) and setting the SR to be "shared".

I have tried this setup for XCP with DRBD primary-primary SR, and it works fine with live migration. From the point of view of xapi, the SR is kind of local (/dev/drbd0), but it still can be shared. This setup is not yet in production (not stress-tested yet), but up to now it works flawlessly.

Agreed. There are a lot of things that need to be done from the xe cli. Remote itself isn't quite so important although I'd stress that one needs to think about layout first of course.



Denis Cardon
Tranquil IT Systems
44 bvd des pas enchantÃs
44230 Saint SÃbastien sur Loire
tel : +33 (0)

Grant McWilliams

Some people, when confronted with a problem, think "I know, I'll use Windows."
Now they have two problems.

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