Re: ASP's that share two RAID Sets

Phil,

I assume that when you say you are using RAID but not mirroring that you
mean you are using RAID-5.  (Mirroring is a level of RAID.  RAID-5 is
checksum w/parity.)  Anyway, if that is the case, then I can't tell you that
you're wrong.  If you lose two drives within an array (at the same time) you
can kiss that array goodbye.  So if you lose two drives in the array 1 then
it affects ASP's 1 & 2.  The same thing goes for losing two drives in array
2.

While you are reviewing your disaster recovery plan be sure to cover the
"What if?" of your system being destroyed (fire, flood, tornado, aggravated
employee w/sledge hammer ;-), etc.).  In this case you would have to recover
the entire system, so your plan should not be dependent upon one ASP being
left in tact.

(And now the company plug...)  The company I work for offers Contingency /
Disaster Recovery Planning services, so if you need some assistance you can
look us up at www.nokuse.com.

If you want some good general guidance you might check out your local
chapter of the Association of Contingency Planners -
http://www.acp-international.com/.

Chuck


----- Original Message -----
From: <prumschlag@phdinc.com>
To: <MIDRANGE-L@midrange.com>
Sent: Thursday, July 26, 2001 4:36 PM
Subject: ASP's that share two RAID Sets


>
>
> With all the commotion over disk drives failing, we decided to review our
Backup
> and Recovery Procedures.  In the process we have raised a question that we
are
> concerned about.
>
> As an example, I will use an abbreviated disk configuration.  All of our
disk
> drives are RAID protected.  We do not use Mirroring.  All of our
production
> libraries are in ASP 1.  We use ASP 2 only for our journal receivers, so
no
> other production libraries are in ASP 2.
>
> RAID ASP  DISK
> SET       UNIT
> 1    1    01
> 1    1    02
> 1    1    03
> 1    1    04
> 1    1    05
> 1    1    06
>
> 2    1    07
> 2    1    08
> 2    1    09
> 2    1    10
> 2    2    11
> 2    2    12
>
> 3    2    13
> 3    2    14
> 3    2    15
> 3    2    16
>
> I know that if I lose any two disk drives from RAID Set 1 then I will have
to
> recover all of ASP 1.  I also know that if I lose disks 07 and 08, I will
have
> to recover all of ASP 1.  My question is this:  If I lose disks 07 and 08,
have
> I also lost ASP 2?
>
> Based on my (limited) understanding of RAID, it appears that if I lose any
two
> disks in RAID set 2, both ASPs are hosed up.  If that is true, it seems
that a
> number one recovery strategy should be to make sure that ASP's do NOT
share a
> RAID set, but I have never seen this in print.
>
>   Somebody, please tell me I'm wrong.
>
> Phil
>
>
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