Re: [Xen-users] XCP Storage

[Grant McWilliams <grantmasterflash@xxxxxxxxx>]

On Mon, Oct 24, 2011 at 2:50 PM, Brett Westover <bwestover@xxxxxxxxxxx> wrote:

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Very nicely written up how-to, thank you for that. I donât think we'd necessarily want to use XCP as our iSCSI target though, because we wouldn't really have resources left for multi-purposing the storage machine. It's nice to know how to do it, if we have a use case for that though.

So, using an iSCSI target for shared storage between our 2-3 XCP hosts would be one option. What are the benefits over using and NAS running NFS (which are usually cheaper)?

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?

The write speeds of NFS stink. On my hosts using an iSCSI Software target SR I get about 50% more disk throughput on writes over an NFS SR. Reads are very similar though. Even if you want to use a CentOS machine to create an iSCSI SR you can follow my tutorial, just skip the part on adding the CentOS repos. There are advantages to an iSCSI Hardware target such as speed but they're not a shared SR type. The shared SR types are NFS and software iSCSI targets. Between the two I'd recommend the latter. Setting up the initiator on the XCP host is equally easy for both types and with my tutorial it's fairly easy to set up an iSCSI Target on another machine.

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.

In the past I did performance articles on the speed of Xen file based images vs LVM and I'll be working on some of the same for XCP regarding the various local storage types, iSCSI and NFS. It won't be done for at least a month though.
Â

Grant McWilliams
http://grantmcwilliams.com/

Some people, when confronted with a problem, think "I know, I'll use Windows." 

Now they have two problems.
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