[OpenAFS] poor out of cache behavior on writing
Nathan Neulinger
nneul@umr.edu
17 Feb 2003 07:47:01 -0600
On Mon, 2003-02-17 at 01:04, emoy@apple.com wrote:
> On Sunday, February 16, 2003, at 06:36 PM, Garance A Drosihn wrote:
>
> > At 5:01 PM -0800 2/16/03, emoy@apple.com wrote:
> >> nfs 0.120u 21.030s 4:19.47 8.1%
> >> afs 0.5G cache 0.100u 517.330s 10:49.84 79.6%
> >> afs 2GB cache 0.060u 20.570s 4:49.58 7.1%
> >>
> >> In these tests, I copy a 1 GB file from the client to the server.
> >> In both NFS and AFS cases, I use the same client and server machines.
> >>
> >> Notice that with the 0.5 GB cache, it takes about 2.5x longer to
> >> copy the file, and consumes almost 80% of the CPU, mostly in system
> >> time. The 2 GB cache case is more reasonable, taking just
> >> slightly longer than NFS.
> >
> > Notice that your cache is half the size of the file you're trying
> > to copy. In the past we at RPI have noticed that AFS performance
> > is bad if the machine has a cache size that is smaller than a
> > file you want to work on.
>
> Yes, that was the point; copying a file bigger than the cache. I
> wanted to confirm that this is expected behavior, especially as bad as
> I am seeing. I hope this can get fixed someday, because files are
> constantly getting bigger.
>
> Of course, disks are getting bigger as well. Is there a limit on the
> size of the cache? I understand files can't be larger that 2 GB, but
> is there some cache size limit at 2 or 4 GB?
Not that I am aware of other than occasional instability. But I don't
know that this has anything to do with the cache size itself. I've had a
15GB one on one of our ftp servers without much trouble for a while.
FYI, I don't believe file size is limited to 2GB any more with current
linux servers and clients, not sure if the largefile support has been
implemented for other systypes or not though.
-- Nathan
------------------------------------------------------------
Nathan Neulinger EMail: nneul@umr.edu
University of Missouri - Rolla Phone: (573) 341-4841
Computing Services Fax: (573) 341-4216