[OpenAFS] Memory cache question

[Paul Blackburn]

Martha.Cofran@cexp.com wrote:

>First I want to thank everyone on this list that's helped me in the past.
>My site went to production last week (finally) and everything is working
>great.
>
>My question:  Is there a way to prevent a file pulled from the AFS server to
>the client from being cached?  I want most stuff to be cached, I just want
>to prevent certain stuff.
>
>AFS is serving catalog images to a mission critical on-line ordering
>web-site.  Speed is essential, so I've got a 500 Mg memory cache on each of
>my web-servers to cache the most frequently used images (done automatically
>at boot so users aren't affected) of the 1Gig that we have.  Management
>wants to tar up all of the images on AFS every night and copy them to the
>web servers, so that if AFS disappears, recovery would only consist of
>untarring the current data and reconfiguring the directory the web server
>pulls from.  I figured the best way to do this is to run a cron routine to
>tar it to a volume.  Then each client can cp the tar from the AFS directory
>to a local directory.  But, if I do this, will the 1Gig tar file completely
>flush all of the real data out of my memory cache?  Is there a better way to
>accomplish this?
>
>Thanks for your thoughts.
>
>Martha Cofran
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>  
>
The obvious way to not access the cache, is to access data outside of /afs.
I would look at using the rsync command to maintain a local disk replica 
copy of
the whole 1gb of images files. Don't mess around with 500 mb. Disk is cheap.
The rysnc command is "clever" because it only copies what it has to copy.
If there are no changes, rsync will copy nothing.

You could run a hourly crontab'ed rsync to keep the local copies up-to-date.

The other comment I would like to make is about "if AFS disappears".
Really, you can build a robust AFS cell with multiple DB servers and
multiple fileservers.
--
cheers
paul                            http://acm.org/~mpb