[Linux-cachefs] Can cachefs be used to cache access to an NFS server which in not always on

[David Howells]

Antony Cleave <antony.cleave at clustervision.com> wrote:

> I am interested in the possibility to use cachefs on a low power system
> with a 2TB drive to cache access to a much larger more power hungry
> system. I would like to set the large NFS node to hibernate or stand-by
> after 90 mins of inactivity and have an always on cachfs node to
> re-export the storage. This would require the cachefs node to be able to
> wake up the nfs server if data is not in the cache using something like
> IPMI or sending a Wake on LAN packet. Is such a configuration possible?
> If so it would make me very happy as having my storage node on 24x7 is
> probably costing me a fortune and this way it could be off 95% of the
> time and automatically turn on when I need it. I don't mind having to
> wait a 30 seconds or so to access files that are not in the cache.

This would be a function of the NFS filesystem rather than fscache.  fscache
tells NFS that the data it asked for wasn't present, and NFS would then access
the server.  If NFS needs to wake the server up at that point, then that would
be up to NFS.  That way the server gets woken up even when an uncached file is
accessed or if there's no cache.

David