RE: RAID, journaling, and ASPs, oh my!

Jeff,

I have read the reply from John and he is dead on with one slight
disagreement. I do believe it is better for recovery to keep a separate
ASP for journal receivers. If you were to loose multiple drives in your
system ASP and have to restore from an old tape, (last nights at end of
business day), you will still have your journal ASP available to roll
transactions forward from the last backup to current. If your journal
receivers are in the same ASP, well they are lost as well, so why bother
journaling. (At least not for recovery but perhaps for auditing only.)

Second point is more of a question, what is your system unit and what is
the RAID card in it? That will dedicate what RAID configuration you can
run. Most controllers can handle 3 or more RAID sets.

Another point is when you add the 8th drive to the existing RAID set, it
will not re-balance your RAID configuration. For example on a 2780 card
with 3 drive cages of 5 = 15 drives, the system built automatically 2
raid sets, one of 9 and the other with 6. 8 of the 9 are striped, and 4
of the 6 are striped. Our 2778 controller has 12 drive and two raid
sets, one of 8 and one of 4, all striped.

FYI We are running a 520 with a 5709 RAID controller with 4 drives all
striped.

You really need to decide what you need from your RAID sets. Best
performance, Most capacity, Most protection. After adding the drive,
see what the system does with it, if it is not what you want, end your
raid then rebuild to meet your requirements.

If you have the capacity and performance in your system ASP, build a
second ASP with 4 drives for your journal receivers. If you are going
the separate ASP route, you can buy smaller, slower drives and save a
few bucks.


Chris Bipes
Director of I.S.
CrossCheck, Inc.

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Jeff Crosby
Sent: Friday, February 08, 2008 6:23 AM
To: 'Midrange Systems Technical Discussion'
Subject: RAID, journaling, and ASPs, oh my!

I'm looking for what is possible, what is desirable, and what is best
practices.

Currently I have 7 drives in the system unit, all in 1 Raid set. I only
have 1 ASP.

Part 1:
When I add the 8th drive into the system unit (making it full), it could
be either 1 Raid set of 8 drives, or (I think) 2 Raid sets of 4 drives
each.
Or am I limited to 1 Raid set? If I have 1 Raid set of 8 drives, I can
lose only 1 drive before I'm toast, but I lose less space to the
striping. If I have 2 Raid sets of 4 drives each, I can lose 1 drive in
each set before I'm toast. These will all be in the system ASP (maybe -
read on).


Part 2:
I also want to get into journaling. From what I read about journaling,
it is better for recovery purposes for journal receivers to be in a
separate ASP. So let's suppose I put 8 drives into the expansion unit.
I want to reserve some drives for ASP2 for journal receivers. There
will be 1 2780 Raid card in the expansion unit. I assume that Raid sets
either cannot (or should not) cross ASP boundaries for recovery reasons.
The possibilities are . . . what? There's only 1 Raid card, does it
support 2 Raid sets? Or am I limited to 1 Raid set? The rest of these
questions assume more than 1 Raid set. One possibility is 2 Raid sets
of 4 drives each, the 2nd to be
ASP2 for journal receivers. But that seems like a lot of space for just
journal receivers. What else should I put in ASP2? Save files? If I
put anything other than journal receivers in ASP2, doesn't that
complicate backup?


Part 3:
If I CAN have more than 1 Raid set in the system unit, but canNOT have
more than 1 Raid set in the expansion unit, what's wrong with taking 4
drives in the system unit, make them a RAID set, and put them in ASP2?