Re: 3Ware 7500-4 Slow

From: Chuck Swiger (cswiger_at_mac.com)
Date: 09/23/05

  • Next message: Achim Patzner: "Re: 3Ware 7500-4 Slow" 
    Date: Thu, 22 Sep 2005 23:05:08 -0400
To: Francisco <francisco@natserv.net>

    Francisco wrote:
    > On Mon, 5 Sep 2005, Chuck Swiger wrote:
    >> Small writes are pretty much the worst-case scenario for RAID-5,
    >
    > Such as mail servers?

    So-so. RAID-5 is okay on a IMAP reader box, it's not so good for a pure SMTP
    relay, especially one that does virus scanning.

    > How about for a DB server which is mostly read only?

    If your DB claims to support a RAID-5 configuration-- some DBs will change
    their caching behavior to avoid thrashing a RAID-5 volume as much-- it might be
    OK. If you're going to run a big DB, you really ought to be designing the disk
    layout according to what the DB vendor recommends.

    >> normal to see a very significant performance drop-- by up to an order
    >> of magnitude-- from the performance of a bare drive.
    >
    > At which point Raid 5 starts to perform better?
    > 6,8,10 drives?

    Better for small writes? Never.
    Although good hardware and lots of RAM to cache with can help a lot.

    RAID systems have bus limitations on how wide they can go in terms of # of
    drives, also in how much real bus bandwidth is available for very wide configs.
         8 drives is a common maximum width.

    > How about RAID 10 for a DB server?

    This is a much better choice, close to ideal.

    > I have been trying to convince the "powers that be" that SCSI would be
    > much better.. but the price difference is just too astronomical for the
    > capacities we need (500GB to 2 TB)
    >
    > Even 10K RPM IDE drives seem like would be a problem since they are
    > mostly small in size.

    Ten 72's would be in the right ballpark, that's about $2000. Ten of the
    cheapest reasonable 80GB ATA drives would be about $800.

    You could always ask:

    "How much is your data worth to your company, again?"

    You can get 146's for about $500 and even 300GB SCSI-3 drives exist. 

    -- 
-Chuck
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  • Next message: Achim Patzner: "Re: 3Ware 7500-4 Slow"

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