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RE: [Xen-users] iSCSI and LVM


From: James Harper [mailto:james.harper@xxxxxxxxxxxxxxxx]
Sent: Tue 15/06/2010 11:33
To: Jonathan Tripathy; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] iSCSI and LVM

> In the case of iSCSI you would just create an iSCSI device for each LV
> of running lvm on top of your iSCSI volume.
> James
> ---
> Does that not mean that I would have to export nearly 600 LUNs?

If you have 600 lv's then yes, and that may well be a better option.
With 600 lv's all running on the same vg, clvm performance if
snapshotting was ever implemented would suck terribly - every time the
lv was written to and the snapshot received a copy of the original
block, all other nodes would need to know about the new metadata change
or they would read bad data from the snapshot.

I don't know what the per-iSCSI-LUN overhead is vs the clvm overhead
though... I guess it depends on how many nodes you have.



Hi James,

I would have 6 nodes running 100 small (6GB HDD/128MB RAM) VMs each. Do you still think that exporting so many LUNs would be a good idea? If I wanted to forgoe "total migration", I could just export 1 big LUN and do LVM in the xen host? And then if the server went down, it would be just a matter of connecting to that big LUN from another xen server?

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