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  1. #1
    Join Date
    Sep 2002
    Posts
    4

    Cool Unanswered: File System Devices with Dsync vs Raw Devices

    This is a simple question, although I do not expect a simple answer:

    Which option would give me better performance: database devices using files with dsync ON vs. Raw Devices?

    Thanks !!


  2. #2
    Join Date
    Aug 2002
    Location
    Madrid, Spain
    Posts
    97
    Probably, files would give apparent better access times,
    as some data not in ASE cache will be found in Unix
    File System Buffer Cache. But the physical memory
    will be poorly utilized, as many FS buffers in memory
    contain the same data than ASE caches. Hence, the
    conclusion is that, unless there's a nice amount of
    unused physical memory, raw devices are better from
    the whole UNIX environment point of view.

    Add, too, a little overhead for file systems.

    Regards,
    Mariano Corral

  3. #3
    Join Date
    Sep 2002
    Posts
    4

    Exclamation

    Yes, I agree, but remember I'm talking about devices created with the DSYNC option turned to ON, which will cause the File System Buffer Cache NOT to be used... The question remains...

  4. #4
    Join Date
    Aug 2002
    Location
    Madrid, Spain
    Posts
    97
    Originally posted by juank8041
    Yes, I agree, but remember I'm talking about devices created with the DSYNC option turned to ON, which will cause the File System Buffer Cache NOT to be used... The question remains...
    This can vary between OS. I know about HP-UX, and
    the File System Buffer Cache cannot be easyly
    bypassed. A licensed OnlineJFS product is required
    to bypass it in HP-UX (Oracle admins know this well)

    Aside from whether writes bypass the FSBC or not,
    reads won't, and they are the most important for the
    above performance problem: once a page is read, it
    remains for a while in both the FSBC and ASE
    cache.

    Regards,
    Mariano Corral

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