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  1. #1
    Join Date
    Oct 2006

    Unanswered: Optimum RAID Config advice please

    Hello -

    I have an SQL Server 2000 DB running on a 5 year old server. It has 5 drives SCSI 10KRPM drives on IBM ServeRAID 4Lx card. I'm maxing it out to 9 on the same backplane (all 10KRPM).

    Not sure the best way to make them count. Here's the particulars:

    1. Current config is:
    Vol1 = RAID1 for OS, swap, and Logging files.
    Vol2 = RAID5 (3 disks) for DB.

    2. The app does heavy writes and use of Temp DB.

    I don't have by-volume stats. This stat excludes backup (taken 3 hours after a daytime reboot). Windows Task Manager shows SQL task and SERVICES.EXE both have physical reads about 15% higher than physical writes. SERVICES.EXE has about 3x the IO count as the SQL task. I assume that's mainly SQL activity.

    Note: Symantec Antivirus (10.1.6) excludes .mdf, .ldf, .bak, and .trn files.

    My question for you: How best to configure the 4 new drives.

    Redundancy is critical, so any non-RAIDed volume is out.

    Option 1:
    Vol1 = RAID1 for OS.
    Vol2 = RAID5 (3 disk) for app DB.
    Vol3 = RAID1 for Sys DBs (Master etc) plus Temp DB. Also OS Swap. Also .BAK scheduled backup files.
    Vol4 = RAID1 for all .ldf files.

    Option 2: Abandon RAID5 due to write penalty (same division of files)
    Vol1 = RAID1
    Vol2 = RAID1
    Vol3 = RAID1
    Vol4 = RAID1
    9th drive = hot swap.

    Option 3:
    Vol1 = RAID1. for OS and .BAK files.
    Vol2 = RAID10 (4 disk). for all .mdf files
    Vol3 = RAID1 for all .ldf files.
    9th drive = hot swap.

    I'm wondering if RAID1 read penalty will outweigh RAID5 write penalty (for 3 stripe RAID5). Will RAID10 advantages outweigh separation of tempDB + System DB on RAID 1 volumes (or RAID5 + RAID1).

    Thank you very much for your esteemed advice.

  2. #2
    Join Date
    Aug 2005
    If you can take the capacity hit, Raid10 (even with TempDB on the same volume) is faster than any Raid5, even faster than if you had an entire separate Raid1 for TempDB.

    We actually had almost this exact conversation with an EMC SAN architect yesterday. We're replacing one of our clusters and have been wrestling with the optimal disk configuration.

    I personally would go with Option 3.

  3. #3
    Join Date
    Jun 2007
    Ohio, USA
    David Maxwell
    Data Integrity? Yeah, I've heard of that...

  4. #4
    Join Date
    Oct 2006
    Thanks so much for the replies! Great link ReadySetStop.

    Jeebustrain - it's not a capacity hit since I get the capacity of 2 drives with either 4-disk-RAID10 or 3-disk-RAID5. It does make me realize my existing RAID5 uses 32GB drives that aren't commonly available anymore. I think that's OK, the bigger drive should downgrade to 32. With a 4GB database, even 32 x 2 is plenty of space to allow for expansion.

    As that link indicates; SQL IO tuning is a deep subject and lacking real data it shouldn't be over-thought. Performance assumptions are too often wrong.

    I'll take your advice and go with Option 3, unless I can find a compatible external solution I can transfer to the next server - probably within 6-12 months (no time right now for the 64 bit testing process). IBM's external solutions all require PCIe slot or list my current server (IBM x235) as incompatible.

    So; it's a $2000 band-aid that'll get the log files off the OS drive and convert the data volume from RAID5 to RAID10. Should help considerably and is the least risky (4 disk RAID10 is known to always trump a 3 disk RAID5 - not the more risky replacement of RAID5 with RAID1). If I decide to spend more on this server; converting the remaining drives to 15K RPM wouldn't even require downtime - just $1500 in drives (I realize all drives downgrade to lowest speed on backplane).
    Last edited by vich; 04-03-08 at 18:13. Reason: added final comment

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