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RE: Storage array advice anyone?

From: Cary Millsap <>
Date: Wed, 15 Dec 2004 13:59:21 -0600
Message-ID: <002c01c4e2e0$94ad17e0$6400a8c0@CVMLAP02>


I think the way to determine whether such ideas have become outdated is to test the idea. However, I would bet that the following are pretty resilient ideas:

Cary Millsap
Hotsos Enterprises, Ltd.
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-----Original Message-----
From: [] On Behalf Of Stephen Lee
Sent: Wednesday, December 15, 2004 9:33 AM To:
Subject: RE: Storage array advice anyone?

I appreciate the discussion on the topic. I think additional considerations on this particular array (Hitachi TagmaStore 9990) are that the "normal" configuration (according to Hitachi) is that the disks are in groups of 8; each group is a stripe with parity; the parity cycles around all drives. When a bad block occurs, the block is NOT replaced by a spare block on the drive, but the drive is failed and replaced by a hot spare, and phone home occurs. Which -- I guess -- is a fairly aggressive drive replacement scheme.

There appears to be agreement that the best performance for most cases (note: most cases) is to stripe everything across all drives. There does appear to be some remaining discussion, from a fault tolerance standpoint, about whether to go strictly with stripe + parity and trust that Hitachi really has worked out the fault tolerance issues, or assume that claims from Hitachi are just a bunch of sales hype and insist on stripe + mirror. Healthy skepticism is useful, but one does not want to be basing that skepticism on outdated ideas. That is what a lot of this comes down to: Which ideas and rules are outdated -- given the capabilities of this new gee whiz hardware -- and which still hold.

The astute reader will note that the stripe + parity is, more or less, raid 5-ish. But yet again, we have a manufacturer who claims that in their case the I/O speed penalty is no longer an issue. In the case of this array, there appears to be some real world experience to support that claim. Any comments from those who know otherwise, are most welcome. Again, another one of those "Have some of the ideas about this become outdated?" sort of thing.


Received on Wed Dec 15 2004 - 14:03:36 CST

Original text of this message