Re: vfs.hirunningspace on a 3ware 8506

From: Jim C. Nasby (jim_at_nasby.net)
Date: 04/21/04

  • Next message: Uwe Doering: "Re: vfs.hirunningspace on a 3ware 8506" 
    Date: Wed, 21 Apr 2004 12:05:56 -0500
To: Uwe Doering <gemini@geminix.org>

    On Wed, Apr 21, 2004 at 12:55:07AM +0200, Uwe Doering wrote:
    > Petri Helenius wrote:
    > >Jim C. Nasby wrote:
    > >
    > >>Has anyone done any testing to see what value of vfs.hirunningspace is
    > >>optimal for a 3ware 8506-8?
    > >>
    > >Do the 3ware controllers actually care about this value due to the
    > >onboard processing and cache? I thought all writes are satisfied
    > >immediately?
    >
    > The controller itself doesn't care, but the kernel does. With the
    > current implementation, the amount of memory associated with outstanding
    > read requests is subtracted from vfs.hirunningspace. With many
    > concurrent read requests there is no reserve left for write operations,
    > so write performance can suffer substantially.
    >
    > This balancing effect is actually intended in order to give read
    > requests some priority, but in high performance systems with fast,
    > caching raid controllers the default value of said variable is too low
    > and therefore poses a bottleneck.
     
    Unfortunately, it seems the 8500 series only has 1.8MB of cache, so it
    seems like the out-of-the-box setting of 1M may not be too far off.

    Is it normally advisable to set vfs.hirunningspace = whatever the
    controller's cache is? 

    -- 
Jim C. Nasby, Database Consultant                  jim@nasby.net
Member: Triangle Fraternity, Sports Car Club of America
Give your computer some brain candy! www.distributed.net Team #1828
Windows: "Where do you want to go today?"
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  • Next message: Uwe Doering: "Re: vfs.hirunningspace on a 3ware 8506"

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