Re: My project wish-list for the next 12 months

On Thu, 2 Dec 2004, Andre Oppermann wrote:

> Scott Long wrote:
>> 5.  Clustered FS support.  SANs are all the rage these days, and
>> clustered filesystems that allow data to be distributed across many
>> storage enpoints and accessed concurrently through the SAN are very
>> powerful.  RedHat recently bought Sistina and re-opened the GFS source
>> code, so exploring this would be very interesting.
>
> There are certain steps that can be be taken one at a time.  For example
> it should be relatively easy to mount snapshots (ro) from more than one
> machine.  Next step would be to mount a full 'rw' filesystem as 'ro' on
> other boxes.  This would require cache and sector invalidation broadcasting
> from the 'rw' box to the 'ro' mounts.  The holy grail of course is to mount
> the same filesystem 'rw' on more than one box, preferrably more than two.
> This requires some more involved synchronization and locking on top of the
> cache invalidation.  And make sure that the multi-'rw' cluster stays alive
> if one of the participants freezes and doesn't respond anymore.
>
> Scrolling through the UFS/FFS code I think the first one is 2-3 days of
> work.  The second 2-4 weeks and the third 2-3 month to get it right.
> If someone would throw up the money...

You might also design in consideration for data redundancy.  Right now
GFS largely relies on the SAN box to export already redundant RAID
disks.  GFS sits on a "cluster aware" lvm layer that is supposed to
be able to do mirroring and striping, but I'm told it's not
stable enough for "production" use.

Sam