Re: [Xen-users] Shared Storage

[Jonathan Tripathy <jonnyt@xxxxxxxxxxx>]

On 25/04/2011 19:57, John Madden wrote:
> > Hands down mamanging LVM is my number one choice. Ideally I would just
> > like to set up the iSCSI connections once and just leave it
> Yeah.  iSCSI a few LUNs from your SAN, cLVM across your nodes (do the 
> iSCSI in dom0), create your LV's and you're done.
> This is really only half the picture though and touches on another 
> level of storage concepts.  What does your backend disk and cache look 
> like? In my clusters, I create two storage pools, one for "fast disk" 
> and the other for "slow disk," then add LUNs from the SAN 
> appropriately.  You should get as granular as you can in performance 
> and use-case terms though to keep the right IOs on the right disks but 
> that may not be practical with your SAN (e.g., if you just have 64 
> spindles in a single RAID-10 or some dumb JBOD or something).
> I guess the message is to think about how you're laying out your data 
> and then align that with how you lay out your disks.  You may squeeze 
> out an extra 5% by going with multiple LUNs versus a single LUN and 
> another 30% by going with FC instead of multi-GbE, but you can gain 
> even more by utilizing the limited i/o of a spindle more effectively.
> John
Thanks for the excellent advice John. Very much appreciated. While I'm 
not able to disclose our disk setup (for commercial reasons), I am 
confident that what I have in mind is good for us, as we have been doing 
this in a non-shared manner (i.e. disks local to the Dom0) for quite 
some time. But yes, as you say, iSCSI will allow for a little bit of 
"fine tuning".
I also need to sanity test CLVM and see how well (or how badly) it 
handles iSCSI lost connections, propagating LVM metadata changes to 
other nodes, etc..
Now onto some testing to see what works out best...

Cheers

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