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  1. #1
    Join Date
    Feb 2006
    Posts
    13

    Unanswered: 2nd Drive for Proformance? - please help

    We are in a production envirnoment using DB2. The loads will vary from time to time and day to day depending on how many orders we have in the system.

    We had a system setup with the primary DB2 application and logs on drive 'C' with the active database on drive 'D'. The active database was the ONLY file or use for the 'D' drive. So I decided to move the 'active database' (not knowing the purpose) to the 'C' drive with everything else using the db2relocatetool. This made imaging the drive a little easiler and it seemed to work well with no issue

    However, 2 times since the move (two-weeks) the system seemed to slow during very heavy production times where several of 50 computers connected to DB2 having their apps were very slow with slow response. However, this (slowness) has happen on rare occasion before but not 2x in two-weeks.

    Does one get better system proformance when the 'active database' is located on a different drive then DB2 itself????? Maybe, this was the original purpose or does it not make a difference? If so I will move it back.

    IBM sServer xSeries 345

    Any other suggestions if this is a borderline load issue while under heavy use?

  2. #2
    Join Date
    Jan 2007
    Location
    Jena, Germany
    Posts
    2,721
    Let's think about what a DBMS is doing with respect to disk I/O. Every INSERT/UPDATE/DELETE/... operation that changes something in the database needs to be logged. The logs are needed to ensure no changes are lost. Thus, logs must be written quite often. Since disk access is about 1000x slower than in-memory access, log-writing can quickly become a bottleneck if the system is misconfigured.

    So here are a few general guidelines:
    • Place logs on a fast disk so that writing to logs does not compete with other disk activities. I would say that pretty much rules out drive C on Windows.
    • Putting data on the same disk as logs is usually a bad idea. My first idea would be to attribute the slow-downs you are experience to your relocation.
    • Partitioning of a single disk doesn't give you any benefit because disk access still competes for the single resource.
    • Use as many physical disks as you can grab. The idea is that multiple disks can be read/written in parallel while a single disk can not.
    • If possible, get disks with a large write cache (but the disk must ensure that the data in this cache is eventually be written permanentely - even in a power outage).
    • Use DB2's automatic storage mechanisms and, if you have a storage system.
    Knut Stolze
    IBM DB2 Analytics Accelerator
    IBM Germany Research & Development

  3. #3
    Join Date
    Feb 2006
    Posts
    13
    Another problem ....

    I went to move my 'active' database back to 'D' from 'C' as it was originally configured:

    db2relocatedb -f movedb.cfg

    ******* movedb.cfg ********
    DB_NAME=prod_ph
    INSTANCE=DB2
    DB_PATH=c:,d:

    This was successful but now I get an error because it is looking for the logs on my 'D' drive .....

    I never moved the logs path but instead only the DB_PATH to the C drive and now I only reversed what I did before from d:,c: to c:,d:

    Any thoughts on why it is looking for my logs on the d: drive now?

  4. #4
    Join Date
    Jan 2007
    Location
    Jena, Germany
    Posts
    2,721
    What is your DB config parameter "Path to log files" set to?
    Knut Stolze
    IBM DB2 Analytics Accelerator
    IBM Germany Research & Development

  5. #5
    Join Date
    Feb 2006
    Posts
    13
    The logs were set to C:\db_logs

    However, the following changed it to D:\db_logs

    DB_NAME=prod_ph
    INSTANCE=DB2
    DB_PATH=c:,d:

    I only wanted to change the DB_Path but I guess the logs 'path' went along for the ride.

    Can I easily change the logs back to C:\db_logs ???

  6. #6
    Join Date
    Jan 2007
    Location
    Jena, Germany
    Posts
    2,721
    Yes, you can change the log path back to C:. Just set "NEWLOGPATH" DB CFG parameter. You have to recycle DB2.
    Knut Stolze
    IBM DB2 Analytics Accelerator
    IBM Germany Research & Development

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