On 12 Feb 2005 04:46:42 -0800, soto.jesus@gmail.com (Jesus) wrote:

>We are in the process of setting up a SAN of 2TBs and we are trying to
>decide between these two systems. EVA3000 permits virtualraid. IBM?
>
>For example, with 14 discs, EVA permits me to make a lun, partition it
>in different raid types to use it in the distinct servers. IBM?


Just FYI, this is not exactly correct in how the EVA configures your
drives. You create disk groups and assign drives to the disk group.
Then you create individual LUNs at whatever size you need, and present
these to the hosts. When you create these LUNs, you specify what
VRAID level you want. All LUNs are spread across all disks in the
group, alleviating the most common bottenecks at the spindle level.

Now, one drawback of the smaller, 14-drive configuration that you have
is that you really can't get perfect protection from *all* failures,
because you have them all on one, or possibly two shelves. VRAID5
will protect you against a single drive failure, but it won't help you
in some other failure circumstances - rare though they may be.

Most all other storage subsystems I've seen are more bus-based in
their configuration - i.e., they don't have true virtualization of the
drives; and they don't automatically level the I/O load spread across
spindles to avoid hot-spots.

That's not to say that other controllers can outperform the EVA in
some workloads. However, many of these must use massive amounts of
cache to get that performance, and cache memory is pretty expensive.

--- jls
The preceding message was personal opinion only.
I do not speak in any authorized capacity for anyone,
and certainly not my employer.