The keyboard of Chuck Hastings emitted at some point in time:
>
>
> I'm working on some software which runs on a workstation cluster. The way
> we are distributing the work on the cluster, each node needs to do a
> significant amount of I/O. Currently, we have the file system that we
> are working on NFS mounted between the workstations.
>
> Not surprisingly, the I/O performance using NFS is very bad. I am looking
> for alternatives to using NFS. The only commercial alternative I am aware
> of us AFS.
>
> I was wondering if anyone has done some performance studies of large I/O
> over AFS [we are reading and writing files in excess of 8MB]. I know a
> little about AFS, and my gut reaction is that it will be better than NFS,
> but still not fast enough for our high performance application. I suspect,
> therefore, that we will need to develop an in-house solution to this
> performance bottleneck. But I was hoping to get some empirical data to
> back up my gut feeling.
Is that large whole-file data transfers or small data transfers on large
files ?
If you have several machines updating small bits in a large file,
then the "performance" is likely to be dominated by the ratio of
your record size to the "chunk size", usually 8 kbytes in NFS and
64 in AFS, with the proviso that AFS is likely to get the
interlocking right.
If you have whole file transfers of 8 Mbyte or so, the dominant
parameter is the network speed, both AFS and NFS are likely to get
whole-file transfer right, and the callback messages for
interlocking that AFS uses will use an insignificant amount of CP
time. AFS may also give advantages from local caching.
Otherwise, you have to go and write a data server for your
application, and use TCP (or UDP) IP-datagrams, sized to be optimal
for the network hardware (1500 bytes for Ethernet, 4odd for FDDI)
Thomas
* email: cmaae47 @ imperial.ac.uk
* voice: +44 171 594 6904 (day), +44 171 385 6540
* fax: +44 171 594 6958
* snail: Thomas Sippel - Dau
* Application Support Group
* The Center for Computing Services
* Imperial College of Science, Technology and Medicine
* Exhibition Road
* Kensington SW7 2BX
* Great Britain
