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Re: [Xen-users] XCP Storage

Hi Grant,

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

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

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

    How does that work?

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

    Can someone point me to some documentation that explains how
    XenServer and XCP handle storage? It seems to be quite different
    than VMware.


    Brett 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.



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

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