ADSM-L

Re: [ADSM-L] Frustrated by slowness in TSM 6.2

2010-10-09 02:54:41
Subject: Re: [ADSM-L] Frustrated by slowness in TSM 6.2
From: Paul Zarnowski <psz1 AT CORNELL DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Sat, 9 Oct 2010 00:37:51 -0400
Rick,

I think their response would be something along these lines...
The XIV can perform better than other traditional arrays because the
[cache miss] I/Os are spread across so many more spindles.  I get that.
But it seems to be that that can break down when the overall I/O load
gets sufficiently high, across all of the spindles.  In an I/O
intensive environment such as TSM, I think this could be more likely
to happen - particularly if you are using XIV for storage pools as
well as for database volumes.

I'm still skeptical about how far it can go.  I can buy that it has
good performance --- for a SATA-based product.  But not compared to a
pure 15K spindle-based product.  Oh, and the SATA drives are larger
than the SAS or FC drives, which doesn't help.

..Paul

At 01:57 PM 10/8/2010, Richard Rhodes wrote:
>> I would be suspicious of having the db on XIV. Do you have any FC
>> or SAS Disk you could try putting the DB on?  I know XIV has lots
>> of CPU & cache, but underneath it all is still SATA. I've heard
>> Marketing types rave about how fast XIV is, even with SATA,
>> because I/O can be spread across many spindles, but I'm not
>> entirely convinced it's as good as 15k FC or SAS.
>
>This is _exactly_ what IBM has not, and seems unwilling, to explain.
>
>Soon after IBM finalized the purchase of XIV, they had a series
>of seminars around the country (usa) about the box. This wasn't some
>little out of the way seminar . . . Moshe (inventor of the box)
>was there and gave much of the presentation.   I attended one - Lets
>just say it was strange!!!   They hammered on "high performance", over
>and over.  They threw up one graph where they claimed 25k iops at
>3ms response time for a "cache miss" workload.  Lets see, cache miss
>means having to go to the spindle to do the I/O.  SATA drives come
>no where close to this response time.  The workload was either
>not cache miss, or, they effectively short-stroked the drive such
>that the heads never moved.  When I questioned this claim I
>got nowhere - just run-around.
>
>Rick
>
>
>
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--
Paul Zarnowski                            Ph: 607-255-4757
Manager, Storage Services                 Fx: 607-255-8521
719 Rhodes Hall, Ithaca, NY 14853-3801    Em: psz1 AT cornell DOT edu

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