Results 1 to 5 of 5
  1. #1
    Join Date
    Oct 2003
    Posts
    11

    Unanswered: Tablespace Extent and Prefetch size calculation for RAID arrays

    Hello All,

    Probably, following question may have already been discussed but i am not able to find a hit in this forum.

    For a RAID array of 3+p drive and stripe size of 64K, what is a good starting point for extent and prefetch size for a tablespace defined on six logical database partitions with one cotainer on each database partition. Each database partition is on it own array group in SAN.

    According to a redbook, "a good starting point would be to set extent size equal to 1 complete stripe of disks in the LUN and for the prefetch size, it must be a multiple of the extent size times the number of arrays underlying your table space.

    Based on the above redbook recommendation, i came up with the

    Extent sz=#disk drives in a RAID array excluding parity*RAID stripe size

    extent size = 3 * 64K = 192K (or) 6 pages (where page size=32K)

    Prefetch size = n * extent size * number of arrays underlying the tablespace

    Prefetch size = 1 * 192 K * 6 = 1152 K (or) 36 pages

    Am i right ? Please reply with your response.
    for a LUN striped
    across a 6+P array, set it to 6*32 K = 196 K.

  2. #2
    Join Date
    Mar 2003
    Posts
    343
    As far as I understand, extent size should be strip size and prefetch size should be the number of containers * stripe size.

  3. #3
    Join Date
    Oct 2003
    Posts
    11
    Thanks for your input on the extent & prefetch size.
    I'm referring to a redbook"Partitioning for Performance in an e-Business Intelligence World" , page 61

    Thanks

  4. #4
    Join Date
    Mar 2003
    Posts
    343
    There's a white paper written in conjunction with EMC - look on DMDD that kind of explains it in detail - however that may be specific to EMC.

  5. #5
    Join Date
    Oct 2003
    Posts
    11
    HI,

    Are you referring to "Best Practices for EMC Symmetrix 8000 with IBM DB2 Universal Database ".

    I will go thru it and get back to you soon.

    Thanks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •