ADSM-L

[no subject]

2015-10-04 17:53:20

I can't answer the majority of these -- but the high-use SSA volumes should be farthest from the adapter (ie, in the middle of the loop). The SSA spec calls for drives to pass on requests to other drives *before* acting upon their own requests, so the heavy I/O activity should not be nearest the SSA adapter.

And yes, this is counter-intuitive!

TomK

    ----------
    From:   Bruce Elrick[SMTP:belrick AT HOME DOT COM]
    Sent:   Thursday, September 03, 1998 7:52 AM
    To:     ADSM-L AT VM.MARIST DOT EDU
    Subject:        Performance/striping/etc.

    Given AIX 4.2.1 or higher on an RS/6000 with SSA disk, would the
    following be a reasonable disk allocation policy for performance and
    reliability?  I put my comments after each.  I welcome other comments as
    well.

    1) Use ADSM mirroring for database and recovery log with mirrorwrite set
    to sequential for both
    - Yes, protection from corruption is the highest goal.

    2) Raw logical volumes for all disk volumes (db, log, & stgpool)
    - JFS adds journaling but only for FS structure changes (inode
    allocation, directory structure changes) and thus prvides marginal
    protection.  The primary advantage of JFS is over other non-journaled
    FS's, protecting you from the need to do long fsck's after crashes.
    - Raw LV's waste some space ((PP size 1MB) for db and log, but this is
    acceptible)
    - JFS adds a (small?) performance hit on top of the LVM overhead.
    - Does JFS add any performance gains via read-ahead and caching that
    aren't realized by raw LV AND are actually useful given the way ADSM
    accesses the volumes (the buffpool and logpool show that the db and log
    is doing its own optimization for disk access)

    3) Use AIX low level striping (software RAID 1) where volume size
    permits
    - I know I can 'dd' (sequential read & write) to SSA striped at close to
    35 MB/s vs what 7-9 MB/s for single disk access; does this benifit ADSM
    given its access patterns?
    - alternately, does one give one volume to each spindle and let ADSM's
    spreading of load across multiple volumes do the trick?

    4) Put which disks nearest to the SSA adapter card; logs first, then db,
    then stgpool?  Or db, log, then stgpool.

    Food for thought...and any input/debate is appreciated.

    Bruce

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