[OpenAFS] Is it possible to prevent caching local files?

Jeffrey Altman jaltman@secure-endpoints.com
Sat, 02 Apr 2011 11:10:43 -0400

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On 3/30/2011 2:11 PM, Milan Zamazal wrote:
> I use OpenAFS from Debian in home environment.
> I connect from the client machine to both a network file server running=

> on another machine and a local file server running on the same machine
> as the client.  I want to cache much data from the network server, so I=

> use a disk cache.  I don't want to cache any data from the local server=

> in the disk cache because this means they are copied from a local drive=

> to the same local drive during transfer, resulting in poor performance.=

> Is there a way to instruct the client to use a disk cache for remote
> files and to use a memory cache (or not to use any cache at all) for
> files stored locally?  Or to solve the problem in another way?

As I am sure you are aware, the AFS client must read/write all data
through the file servers via the AFS3 RPC protocol in order to perform
authentication and enforce access rights.  Given the current
implementations of the AFS client there is no method by which the AFS
client can access the content of AFS volumes directly.

Data stored in AFS volumes is location independent from the perspective
of the client.  The volumes are permitted to move between servers while
in use.  As such there is no concept of local versus remote data.

As Marc points out elsewhere in the thread, the 1.6 branch contains
"cache bypass" function which permits the AFS cache manager to read data
and avoid storing it in a local cache.  However, even if the cache
manager could avoid caching data only read from the local file server
there would be a significant overhead associated with the local reads
compared to reading from a local disk file system.

I would like to hear a better description of your use case.  Why is
there an AFS file server running on a client machine that is a heavy
consumer of data stored in AFS volumes on the file server?  Perhaps AFS
as it is implemented today is not the best choice of a file system for
your application.

Jeffrey Altman

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