vfs.hirunningspace on a 3ware 8506
Jim C. Nasby
jim at nasby.net
Wed Apr 21 10:06:08 PDT 2004
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
> 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 at nasby.net
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