On Sat, 27 Mar 1999, Luke Mewburn wrote:

>Chris Jones writes:
>> As I understand it (which understanding may be orthogonal to reality),
>> the prestoserve card was originally used to cache NFS writes.  One of
>> the ideas thrown around in the discussion I mentioned, though, was
>> caching all metadata, in addition to NFS writes, on the card.  The
>> could theoretically give you some really spiffy filesystem
>> performance.
>
>As far as I understand it, presto doesn't just `cache NFS writes'. It
>actually caches all synchronous writes to the local disk (which writes
>from the NFS server daemon are, to comply with the NFSv2 spec).
>Metadata writes happen to be synchronous too, so they get a speedup as
>well.

Indeed.  I remember poking about on a SunOS 4.1.3 system after running
the wonderfully-named presto_chango script which modified the kernel
build files to use the prestoserve.  It hooked the disk driver I/O
routines in the device switch.  Sun used to claim that it speeded up
local disk access as well (and by default it would accelerate all
filesystems, including / /usr and /var), although we never bothered
trying to measure the performance enhancement.


Roger

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