[CentOS] iSCSI best practices

Sat Dec 10 18:49:57 UTC 2011
James A. Peltier <jpeltier at sfu.ca>

----- Original Message -----
| Hey folks,
| I had some general questions and when reading through the list
| archives I
| came across an iSCSI discussion back in February where a couple of
| individuals were going back and forth about drafting up a "best
| practices"
| doc and putting it into a wiki. Did that ever happen? And if so, where
| is it?
| Now my questions :
| We are not using iSCIS yet at work but I see a few places where it
| would be
| useful e.g. a number of heavy-use NFS mounts (from my ZFS appliance)
| that I
| believe would be slightly more efficient if I converted them to iSCSI.
| I
| also want to introduce some virtual machines which I think would work
| out
| best if I created iSCSI drives for them back on my Oracle/Sun ZFS
| appliance.
| I mentioned iSCSI to the guy whose work I have taken over here so that
| he
| can concentrate on his real job, and when I mentioned that we should
| have a
| separate switch so that all iSCSI traffic is on it's own switch, he
| balked
| and said something like "it is a switched network, it should not
| matter".
| But that does not sit right with me - the little bit I've read about
| in the past always stresses that you should have it on its own
| network.
| So 2 questions :
| - how important is it to have it on its own network?
| - is it OK to use an unmanaged switch (as long as it is Gigabit), or
| are
| there some features of a managed switch that are desirable/required
| with
| iSCSI?
| thanks,
| -Alan

It is not imperative to have a separate switch but it certainly helps, especially if your switch is not managed.  Managed switches will allow you to create VLANs that can be both jumbo frame and non-jumbo frame on the same device.

Jumbo frames is really the important thing when it comes to iSCSI.  Having 9000 byte packets verses 1500 byte packets will dramatically increase your performance per interrupt.  Most cheaper unmanaged switches cannot do this.

Second, if their cheap switches, you'll likely saturate the backplane no matter what.  Get good switches for this type of work.

James A. Peltier
Manager, IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 778-782-6573
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices
I will do the best I can with the talent I have