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Re: [Xen-users] Xen + SAN

  • To: "Fajar A. Nugraha" <list@xxxxxxxxx>
  • From: Rudi Ahlers <Rudi@xxxxxxxxxxx>
  • Date: Fri, 24 Jun 2011 09:42:21 +0200
  • Cc: Simon Hobson <linux@xxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 24 Jun 2011 00:43:58 -0700
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On Fri, Jun 24, 2011 at 9:17 AM, Fajar A. Nugraha <list@xxxxxxxxx> wrote:
> On Fri, Jun 24, 2011 at 2:03 PM, Simon Hobson <linux@xxxxxxxxxxxxxxxx> wrote:
>> Fajar A. Nugraha wrote:
>>> If you need SAN for other purposes (e.g. live migration), then others
>>> have already provided some good example. However, personally I'd check
>>> again with the requirement. It's possible that the "best" setup for
>>> you might be:
>>> - a zfs-based storage appliance (e.g. napp-it, nexentastor) with lots
>>> of disks (mirror), lots of memory, and SSD for L2ARC/SLOG to provide
>>> high I/O throughput
>>> - nfs and image-based disks to provide easy management
>>> - tap:aio or tap:vhd on Xen side
>> Do you have any feeling for how such a setup might compare, performance
>> wise, with a local disk setup with the same disks and LVM and a partition
>> per client block device ?
> Local disk with block devices should definitely be faster.
> But here's the catch: notice I specifically suggest zfs, lots of
> memory, and SSD?
> zfs/zvol by itself has lower performance compared to plain block
> device. 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.
> ... or if you have the money, simply buy EMC/Netapp-base/Oracle
> storage with cache SSDs :D
> --
> Fajar
> _______________________________________________


Isnt's there a way to use a local SSD drive as cache, when using a SAN?

As matter of interest, you can store the EXT3/4 journal on a separate
SSD drive to improve performance a bit, but it's not nearly as
effective as using SSD for ZFS's ZIL + L2ARC cache drives.

Kind Regards
Rudi Ahlers

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