RE: [Xen-users] Large server, Xen limitations

["Robert Dunkley" <Robert@xxxxxxxxx>]

My own experience has been a decent raid controller is more important. 

If you have multiple disk reads and writes happening from multiple VMs
then a good controller like an Areca or 3Ware will put the request in
blocks to stop disk thrashing, it can make a big difference. Even raid 1
read performance was better on the Areca SAS card we used compared to
the onboard LSI SAS solution because Areca seems to be better at raid 1
read interleaving. A good SAS card also allows you to mix and match SAS
and SATA.

As a general rule of thumb an enterprise 15K drive will offer 2-3 times
the performance of SATA 7.2K drive, the reason is partly because of the
spindle speed but also partly due to disk firmwares being geared for
server random read / write patterns rather than continuous / read ahead
home user loads. 

We actually mix and match as needed, generally I found SAS is worth it
for database and web servers but a waste on web servers or backup NAS.
SATA is also available in much larger sizes.

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