[CentOS] iSCSI best practices

Fri Dec 9 17:36:59 UTC 2011
Les Mikesell <lesmikesell at gmail.com>

On Fri, Dec 9, 2011 at 10:27 AM, Alan McKay <alan.mckay at gmail.com> wrote:
> 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.

This doesn't directly apply, but this nfs appliance vendor wants you
to think that nfs isn't as bad as you might think:
Overcommitting for de-dup/compression  might be harder with iscsi -
resizing filesystems would be a lot harder.

> 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".

Is it a single switch?  Otherwise you share the bandwidth on the trunk

>  But that does not sit right with me - the little bit I've read about iSCSI
> 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?

I've seen recommendations to use jumbo frames for iscsi - and if you
do that, everything on that subnet needs to be configured for them.

   Les Mikesell
     lesmikesell at gmail.com