Re: 3310 RAID1 (mirror) Question

In article <1150288691.925660.262540@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"Joe D." <newbie_from_newbie@xxxxxxxxx> writes:
Good morning, gentlemen! A very interesting post.

I am about to set up a 3310 (probably a 3320, actually, but I presume
they are essentially the same as far as config goes?).

Pretty well. The 3320 is Ultra320, while the 3310 is Ultra160. And they
do take different firmware (new patches for both were released today)
so don't try applying 3310 firmware to a 3320 (or vice versa). But as
far as configuration goes I haven't noticed any differences.

I presume from
the post that you both have the RAID controller option. We're not going
to go with the RAID controller, due to cost considerations. Rather, I
was planning on simply using SVM for the system's boot disks, and use
the 3310's disks via raw access for a Sybase database.

I wonder if I could trouble you to elaborate a little on some points
made earlier:

Peter Said:
The 3310 will only give you a single host connection. (You could
connect another host to the array, or even the same host more than
once, but there isn't any way to get path redundancy and failover.)

Given two controllers, if one fails then it will just use the
other. Automatically and transparently. Works great. No interruption to
service.

and later when BD noted that he had 2 SCSI connections to the array and
was seeing 2 disks:

.... disconnect the SCSI cable from the
host. You don't really want this to be accessible, as it's just asking
for trouble.

One of the things I was hoping for in purchasing these arrays was the
dual-path redundancy (which it sounds like I'm not gonna get).

Well, SCSI is intrinsically single-path - unlike FC disks which are
dual-ported. So with JBOD you could have one path to a disk and a
different path to its mirrored (on the host) partner.

Is this
to say then, that even if I order a pair of PCI SCSI cards that I
shouldn't connect both of them?

With a RAID controller, you shouldn't. With JBOD, you should, and split
the busses so you attach half the disks to one card and half to the other.

My past experience had been with
Veritas which recognized automatically 2 paths to the same disk(s) and
presented you with only the one, even though you could see both from
format.

That's a good point. I hadn't thought about Veritas (previous
experience makes my mind blank it out - oh the pain!). I don't actually
know what Veritas would do with it.

I realize we may be talking apples and oranges here since you're using
the RAID controller (again, I'm presuming) and we won't be, and also
we'll be accessing them as raw devices, but is what I'm planning
feasible/recommended? Any alarm bells going off in your heads?

If you take out the raid controller, then I would run with a dual-bus
configuration. Connect one half of the disks to one card, the other
half to the other card, and then create mirrors (either SVM or within
Sybase) between disks on the two controllers.

In other words, split it in half and treat it as two 6-disk arrays that
happen to be in one box.

Note that the rules for JBOD and the rules for RAID are different.

--
-Peter Tribble
L.I.S., University of Hertfordshire - http://www.herts.ac.uk/
http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/
.

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