[geeks] Xserve RAID is out... kind of nice

[Scott Howard]

On Mon, Feb 10, 2003 at 01:36:18PM -0500, Andrew Weiss wrote:
> http://www.apple.com/xserve/raid/

Hmm.. looks OK, until you start digging...

The drives are 180Gb - but only 7200RPM which will hurt performance.
The drives have the on-drive cache enabled - which isn't battery backed.
128Mb->512Mb cache per controller - but it's not mirrored.
FC-AL interface - but with a copper connector (ie, they are NOT Fibre)
72 hour battery backup for the cache - but it's not standard.

The lack of a battery as standard means that either the cache runs in
write-through by default (which _really_ kills RAID-5 performance), or
they are risking serious data loss. (Without a battery, a power outage
basically means you reformat the entire array and restore from backups).
They don't mention which of these two options they have taken by default,
but I hope like hell it's the first.

Also looks like they screwed up the Electrical Requirements section - they
say "Maximum input current: 3.5A (90V to 132V) or 7.1A (180V to 264V)"
which doesn't make a lot of sense (higher voltage leads to lower amps for
a fixed power requirement, not the other way around)

As for using ATA drives, I suppose time will tell if that turns out to
work or not. They are never going to get some of the advantages of FC-AL
(in particular, dual ported drives), but this is sorta being worked
around by having one drive/controller. As wrong as this seems, it probably
does give roughly equivalent performance/reliability to SCSI (as long as
they are using tag queueing?), but not the same as FC-AL.

For the density, it's only about the same (or less) than what others
are releasing.  Sun's new arrays do 1.72Tb in 2U, and thats without having
to resort to 180Gb/7200PRM disks like Apple has. (Sun is 12 drives in 2U,
Xserve is 14 drives in 3U)

So price is really the only thing it's got in it's favour, and some (but
defintiely not all) of that price difference is going to disappear by
the time you add in batteries, fibre GBIC's and a larger cache (to
bring it up to the spec of the arrays they are comparing it to).

  Scott.