ADSM-L

Re: Dsmfmt on cx600 any thoughts?

2004-02-21 06:29:17
Subject: Re: Dsmfmt on cx600 any thoughts?
From: Roger Deschner <rogerd AT UIC DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Sat, 21 Feb 2004 01:39:01 -0600
I moved our large AIX ITSM 5.1 server to Raw Logical Volumes without
suffering any loss of performance. Migration still runs at about the
rated speed of the S-DLT tape drives. The database is, if anything,
slightly faster. With RLVs, the application (ITSM) is closer to the
hardware, so there is less to protect you against mistakes in your I/O
configuration. Not anything esoteric, just good Best Practices in I/O
confiuguration management. Spread the load out among as many disk heads
and I/O channels as possible, and watch out for bottlenecks.

One gotcha in this regard is if the volumes in a diskpool are radically
different sizes, watch out for an I/O bottleneck on the larger volumes
as the pool fills up. That's because the smaller volumes will fill
completely, shifting the active I/O load entirely to the larger volumes.
Circumvent this by combining smaller PVs into larger RLVs (using
striping of course) that will more or less match your larger PVs. You do
not need to match the sizes exactly.

The IBM manuals warn you repeatedly about the dangers of Raw Logical
Volumes. If you enlarge one, the TSM data within it is destroyed. This
danger can be partially avoided by setting the Max LPs to the same as
the current LPs. That way at least there's a safety latch on the gun
pointed at my foot - I would have to change two things.

This thread started with slow performance of dsmfmt, and that is where
the greatest performance advantage of RLVs is - you don't run dsmfmt at
all! Even if RLVs were slightly slower, which I do not believe is true
if you put a little management effort into it, I'd still use them
because of the amount of MY time they save.

Roger Deschner      University of Illinois at Chicago     rogerd AT uic DOT edu


On Sat, 21 Feb 2004, Paul Ripke wrote:

>On Friday, Feb 20, 2004, at 09:16 Australia/Sydney, Justin Bleistein
>wrote:
>
>> according to the aix tsm server performance manual it states that it
>> rlv's
>> may buy you performance in client backup and restore operations but
>> not in
>> server data movement operations such as migration.
>
>OK, I haven't touched TSM on AIX for 4 or so years, but when I migrated
>our two Sun TSM servers from ufs to raw VxVM volumes, I didn't notice
>any degradation in any aspect of TSM operations. I'm somewhat surprised
>that there would be a degradation of performance for operations like
>migrations using raw LVs on AIX...
>
>Cheers,
>--
>Paul Ripke
>Unix/OpenVMS/TSM/DBA
>I love deadlines. I like the whooshing sound they make as they fly by.
>-- Douglas Adams
>

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