Re: [Xen-users] Xen + SAN

[Javier Guerra Giraldez <javier@xxxxxxxxxxx>]

On Fri, Jun 24, 2011 at 2:17 AM, Fajar A. Nugraha <list@xxxxxxxxx> wrote:
> However it's also the only filesystem that I know of that can
> use SSD to speed up both read and write. It's something that LVM/ext4
> can't do. So it just might be able to offset performance penalty of
> zfs + nfs + file-based-image.

there are a few SSD cache projects for
Linux(https://github.com/facebook/flashcache,
http://bcache.evilpiepirate.org/,
http://users.cis.fiu.edu/~zhaom/dmcache/index.html), these operate at
block level, accelerating any block device.  while the obvious place
to put them is in the target box, i've been thinking about using on
the initiator boxes, to accelerate the iSCSI LUNs :

obvious:

harddisks ==> RAID/LVM ==> SSD ==> iSCSI target-----(network)--->
iSCSI initiator ==> Xen VM

food for thought:

harddists ==> RAID/LVM ==> iSCSI target ----(network)---> iSCSI
initiator ==> SSD cache ==>Xen VM


this is feasible for VM images, since each LUN is used by only one
machine at a time.  clustered filesystems would immediately choke on
such a setup.

pros: could be _much_ faster, since the cache is local to the user.
cons: you have to flush/disable the cache while live-migrating


it's still just an idea, i haven't found the time (nor machines) to
test it.  but sounds doable, no?

-- 
Javier

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