[OpenAFS] poor out of cache behavior on writing

[Nathan Neulinger]

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