[Beowulf] SATA II

[Geoff Jacobs]

Mark Hahn wrote:
>>> Thanks Peter,
>>> But do you mean that SATA is not a suitable choice for a beowulf
>>> cluster?
>> SATA is fine. You just have to be choosy about the SATA/SAS controller,
> 
> it's interesting that SAS advertising has obscured the fact that SAS is
> just a further development of SCSI, and not interchangable
> with SATA.  for instance, no SATA controller will support any SAS disk,
> and any SAS setup uses a form of encapsulation to communicate with
> the foreign SATA protocol.  SAS disks follow the traditional price
> formula of SCSI disks (at least 4x more than non-boutique disks),
> and I suspect the rest of SAS infrastructure will be in line with that.
Yes, SAS encapsulates SATA, but not vice-versa. The ability to use a
hardware raid SAS controller with large numbers of inexpensive SATA
drives is very attractive. I was also trying to be thorough.

>> and be mindful of reliability issues with desktop drives.
> 
> I would claim that this is basically irrelevant for beowulf.
> for small clusters (say, < 100 nodes), you'll be hitting a negligable
> number of failures per year.  for larger clusters, you can't afford
> any non-ephemeral install on the disks anyway - reboot-with-reimage
> should only take a couple minutes more than a "normal" reboot.
> and if you take the no-install (NFS root) approach (which I strongly
> recommend) the status of a node-local disks can be just a minor node
> property to be handled by the scheduler.
PXE/NFS is absolutely the slickest way to go, but any service nodes
should have some guarantee of reliability. In my experience, disks
(along with power supplies) are two of the most common points of failure.

-- 
Geoffrey D. Jacobs

Go to the Chinese Restaurant,
Order the Special