FAQ
hi


there are two sections in statspack for IO related information.


under load profile
- physical and physical writes per second
under tablespace IO /File IO
- avg reads/sec and avg writes/sec


what is the difference between the above and which one is related to IOPs


thx
sai

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  • Paul Drake at Feb 23, 2005 at 10:58 pm
    imagine if you have the following storage subsystem constructed:
    (ignore caching effects for this little thought experiment)

    volA: 3 disk RAID 5 volume mounted over single pathed 1 Gbps Fibre, 32
    KB stripe size
    volB: 8 disk RAID 10 volume mounted over dual pathed 2 Gbps Fibre, 256
    KB stripe size

    db_block_size=8192
    db_file_multiblock_read_count=32

    Imagine that you have 2 datafiles per tablespace, an LMT tablespace
    with uniform size of say 1MB and have 2 GB of data loaded in it, 1 GB
    in 1 datafile mounted on volA, 1 GB in 1 datafile in volB.

    When you view the io waits by tablespace, they will appear to be
    mediocre based upon the averaging of the superior performance of the
    IO to volB hampered by the incredibly awful performance of volA.

    When you view the io waits by datafile, you can see the difference in
    the io characteristics (on average) by datafile. IO waits would likely
    be under 2 ms for the RAID 10 vol, around 20 ms for the RAID 5 volume.
    Throughput would be proportionally similar.

    You then recite some explitive about RAID 5, move all the datafiles to
    volB and swear off ever discussing RAID 5 again.

    This little comment will probably get me tossed out of BAARF. so be it.

    Paul

    On Wed, 23 Feb 2005 16:46:18 -0800 (PST), Sai Selvaganesan
    wrote:
    hi

    there are two sections in statspack for IO related information.

    under load profile
    - physical and physical writes per second
    under tablespace IO /File IO
    - avg reads/sec and avg writes/sec

    what is the difference between the above and which one is related to IOPs

    thx
    sai

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postedFeb 23, '05 at 7:49p
activeFeb 23, '05 at 10:58p
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Paul Drake: 1 post Sai Selvaganesan: 1 post

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