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Simon · Guest

Hi,

Am considering recommending purchase of either an IBM DS300 or DS400
storage system for our environment. I've done a little reading on both,
and understand the obvious differences (e.g. iSCSI for DS300, Fibre for
DS400, more disks for DS400 etc), but I'd appreciate some advice on the
specifics in relation to my targeted use.

It is for a production environment, in which we have a document server,
storing and retrieving relatively large files (2-5MB) on a storage
system. It is the storage system that I need to advise on, and I'm
having some trouble understanding why I should double the price to get
the DS400 if the only benefit is larger disks, and potentially higher
channel data rate through fibre.

Isn't it still running on a single SCSI bus to the disks? That's
320Mbps, so I'm only going to get increased performance when hitting
the cache I assume?

My most pressing concern is path redundancy from the storage server, to
the storage system. In both the DS300 and DS400 case, I would be
recommending a dual controller configuration, and we would run dual
connections over dual HBAs on the server, but in the documentation for
the devices, only the DS400 shows a dual path configuration in the
context of path redundancy. The DS300 is only shown in the context of
improved performance brought about by having two iSCSI links between
the server and the system.

Is anyone aware of whether the DS300 can be configured so that if one
controller dies, the server will still have uninterupted access via the
2nd controller?

In both the case of the DS300 and DS400 is there special software that
needs to be ordered to configure multi-pathing on the server HBA's
(sorry if my terminology is incorrect). i.e. Is there software that I
need to run on the xServer that will tell the HBAs to configure for
redundancy in event of single path failure?

Also can anyone confirm whether or not the caches are mirrored?

Thanks
Regards
Simon

carmelomcc · Guest

Do not buy either one wait for IBM to ramp up the NetApp OEM and
purchase a Filer. They are much more reliable then the IBM internal
line of storage.

Arne Joris · Guest

The interoperability guide
(http://www-03.ibm.com/servers/storage/disk/ds/pdf/ds300400_interop.pdf)
states that the DS300 does not support any fail over (path nor
controller) in direct attach, you need a switch in between your hosts
and the DS300. Depending on the pice of the GiGE switch, you could
save some money by direct-attaching the DS400 to your server, since the
IBM drivers for FIbre Channel will do both path, HBA and controller
fail over in that configuration.

The driver appears to be the standard Qlogic FC failover driver, so I'm
not sure multi-pathing (as in using both paths to a volume for enhanced
performance) is possible, just path and hba failover.
My guess would be all volumes are exported from both controllers, and
for Linux, bot paths are listed as the active path. The QLogic HBA will
pick one path (or you can configure it to pick a preferred path) and if
the path fails, go to the other path.
You'll still get better performance by having two controllers by tuning
the HBAs to pick their preferred path for a set of volumes to different
controllers (assuming you have more than one volume of course,
otherwise there'll be no performance improvement).

Rob Turk · Guest

"carmelomcc" <carmelo.mccutcheon@gmail.com> wrote in message
news:1132847254.122705.324510@g49g2000cwa.googlegroups.com...

Simon · Guest

Great. Thanks for the info. Felt the DS400 was likely to be the way to
go. Glad you could fill in the blanks. We are going for QLogic HBAs so
we're definitely on the right track there. Only one volume required for
this application, and direct connection from the server to the storage
device, so we'll need to consider path configuration while building.
Good food for thought. Cheers
Simon

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