[OpenAFS] poor out of cache behavior on writing

[Paul Blackburn]

Sven,
I have seen that using a 256mb RAM cache on a machine with 1gb RAM
running AIX did not crash.
--
cheers
paul                       http://acm.org/~mpb

Sven Oehme wrote:

>
> hy ,
>
> i have seen increasing the memcache size >50 mb on a Linux Server with 
> 512 mb that afs is crashing .
>
> Sven
>
>
>
>
> *Paul Blackburn <mpb@est.ibm.com>*
> Sent by: openafs-info-admin@openafs.org
>
> 02/18/2003 10:06 AM
>
>        
>         To:        Edward Moy <emoy@apple.com>
>         cc:        openafs-info@openafs.org
>         Subject:        Re: [OpenAFS] poor out of cache behavior on 
> writing
>
>        
>
>
>
> Edward Moy wrote:
>
> >
> > Yes, it is true that fast read performance should be a higher
> > priority. But if I want to read a 1 GB file from AFS, I have to write
> > it there in the first place.
> >
> > Look at the times to read that same 1 GB file:
> >
> > nfs 0.050u 18.050s 2:25.59 12.4%
> > afs 0.5GB cache 0.030u 10.300s 2:29.26 6.9%
> > afs 2GB cache 0.030u 11.250s 2:32.67 7.3%
> >
> > Within the normal fluctuations in the network itself, AFS is very
> > close to raw NFA, for first-time reading. But also note that even when
> > the cache is smaller than the file, one does not see the poor behavior
> > exhibited in the write case.
>
> Hi Edward,
>
> I think you have succintly made the point that you need to size
> your AFS cache appropriately for your workload.
>
> If you plan on working with 1gb files often and writing 1gb files
> into /afs/@cell/$whatever/ then you better configure a big enough AFS 
> cache.
>
> I think that "cache thrashing" is similar to "page thrashing"
> in virtual memory operating systems. It is a situation that
> occurs when there is not enough resource allocated (eg cache too small)
> for the workload applied to it.
>
> Remember also that with AFS, you have a choice of disk cache
> or RAM cache. So if you have enough installed RAM, you
> will see faster access using AFS RAM cache (than using disk cache).
>
> >
> >
> > It takes 2 1/2 minutes to read the file, and 4 minutes to write it
> > when there is enough cache. But as a user, when that goes up to 10
> > minutes, and uses 80% of the processor, my first reaction would be
> > that something is wrong.
> >
> > From other comments I've seen, it appears that this is "expected"
> > (though hopefully not desirable) behavior. I just wanted to point out
> > that there is room for improvement in this area.
>
> You are absolutely right to point this out.
> If there is something "not working right" with AFS write function
> then this is a good place to discuss it and propose solutions.
> --
> cheers
> paul http://acm.org/~mpb
>
>
> _______________________________________________
> OpenAFS-info mailing list
> OpenAFS-info@openafs.org
> https://lists.openafs.org/mailman/listinfo/openafs-info
>