[mythtv-users] Is there a distributed filesystem available?

Tony Lill ajlill at ajlc.waterloo.on.ca
Thu Jun 22 03:48:31 UTC 2006


Matthew McClement <mythtv at macker.co.uk> writes:

> Tony Lill wrote:
>> I think your main problem is the directory heirarchy imposed by the
>> coda design is incompatable with the flat filespace that mythtv
>> wants. I'm sure that you can get around that with symlinks, but if you
>> go that route, then you may as well use automount and nfs. That's what
>> I'm using, and, aside from not being able to use autoexpire, it works
>> pretty good.
>
> An alternative to using symlinks is to use Unionfs to achieve a flat 
> directory structure from several mount points. However, it has no 
> knowledge of fault tolerance and should a disk die, you'll have to 
> manually break the union and remove the broken device.

I looked into this a while ago. As with lvm, you also agregate all the
problems of the underlying filesystems. Aside from local disk
failures, if any of them are nfs mounts, then add network and host
problems to the list of things that can take it down. 

> The other issue is that, AFAIK, only one member of the Union is 
> writable(although it looks like you can still delete files from 
> "read-only" volumes). You could potentially get around this by having a 
> cron script rotate the union membership every night(after making some 
> basic checks so ensure that there is enough space and no recordings are 
> taking place at the that time).

Yeah, writes only happen to the filesystem on top of the stack. When I
was mucking about with it, I submitted a patch to allow you to
reshuffle the disks atomically without taking the union apart, and
someone else submitted one to space ballance the members. I don't know
if they've included any of these in the latest version, though.

I gave up, since unionfs had it's own bugs that made it unuseable.
--
Tony Lill,                         Tony.Lill at AJLC.Waterloo.ON.CA
President, A. J. Lill Consultants        fax/data (519) 650 3571
539 Grand Valley Dr., Cambridge, Ont. N3H 2S2     (519) 241 2461
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