[mythtv-users] Network storage fault tolerance (was Re: Myth autoexpiring brand new shows)
rogerheflin at gmail.com
Tue Aug 26 23:47:35 UTC 2008
David Brodbeck wrote:
> Michael T. Dean wrote:
>> Speaking of which, does anyone know of a way to make NFS tolerant of the
>> NFS server's going down so that it will automatically unmount/remount
>> the filesystems?
> Technically NFS is stateless -- if a server goes down, I/O requests on
> that filesystem just hang until it comes back. No need to remount.
> This usually isn't what people want, though, because it leads to lots of
> applications sitting around in unkillable D states.
Given the D state, and given having intr set on the mount, it should be possible
to have an application always be setting up a timer and detect the hang (with a
signal handler getting a timer expired signal) and possibly do something about
it either move to another machine or put data on a local disk until things come
back. To make it truly tolerant things would need to be threaded in such a way
that writing to the final disk would not stop the recording and could be
buffered on local disk and then put back to the nfs server when it came back,
then at least in that case with a reasonable amount of local disk (say 30-60 GB)
one could buffer quite a lot and fix the nfs server when it was noticed.
Though this would not be terribly helpful if the NFS server and the backend were
the same machine (though if it were fixed before the next recordings came up it
would be possible to not lose any record data).
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