[CentOS] iSCSI disk preperation

[Dr. Ed Morbius]

on 16:28 Tue 08 Feb, Jason Brown (jason.brown at millbrookprinting.com) wrote:
> On 02/07/2011 05:09 PM, Dr. Ed Morbius wrote:
> > on 15:19 Mon 07 Feb, Ross Walker (rswwalker at gmail.com) wrote:
> >> On Mon, Feb 7, 2011 at 2:36 PM, Dr. Ed Morbius <dredmorbius at gmail.com> wrote:
> >>> on 13:56 Mon 07 Feb, Jason Brown (jason.brown at millbrookprinting.com) wrote:
> >>>> I am currently going through the process of installing/configuring an
> >>>> iSCSI target and cannot find a good write up on how to prepare the disks

<...>

> >>> What are you using for your iSCSI target (storage array)?

<...>

> >>> Truth is, there's a lot of flexibility with iSCSI, but not a lot of
> >>> guidance as to best practices that I could find.  Vendor docs have
> >>> tended to be very poor.  Above is my recommendation, and should
> >>> generally work.  Alternate configurations are almost certainly possible,
> >>> and may be preferable.
> >>
> >> If a best practices doc could be handed to you right now, what would
> >> you like it to contain?
> > 
> > <grin>
> > 
> > I've got about 35 pages of that document sitting on my local HD now.
> > Negotiating with management about releasing some of it in some form or
> > another.

<...>

> >> I would be happy to draft something up and put it on a wiki somewhere,
> >> but I would need a list of talking points to start with.
> >  
> > How's this do you?
> 
> In our configuration, we are going to have our iSCSI targets and
> initiators all connected to the same layer 3 switch and isolate the
> iSCSI traffic on separate networks.  Would it be beneficial to also set
> up multipath for this as well?

That's pushing the limits of my knowledge/understanding.

Multipath aggregates multiple pathways to a data store.  In the case of
the Dell equipment mentioned in my post, there are two controllers, with
4 TOE/NIC cards each, offering 8 pathways to each target storage LUN.

Multipath aggregates all 8 pathways to a single target, and provides
both performance and availability enhancements by utilizing these
pathways in turn (defaulting to round-robin sequencing), and presumably
disabling use of any pathway(s) which become unavailable (whether or not
any monitoring/alerting of this failover/fail-out is possible would be
very useful to know).

It's also possible to configure multiple initiator pathways, though in
our case we've already aggregated multiple NICs into a bonded ethernet
device.

From the description you've provided, I don't think you've got a
multipath configuration.  I don't know what would happen if you
attempted to set up multipath, but presuming not too much magic smoke
escapes, I'd be interested in finding out.

Presumably you'd have to configure /etc/multipath.conf appropriately to
pick up the target(s).

-- 
Dr. Ed Morbius
Chief Scientist                             When you seek unlimited power
Krell Power Systems Unlimited                       Go to Krell!