[tech] morwong's disks

[Grahame Bowland]

On Wed, 2003-08-13 at 22:37, Nick Bannon wrote:
> On Wed, Aug 13, 2003 at 10:03:28PM +0800, James Andrewartha wrote:
> > Morwong now has 5x 9gig and 1x4 gig disks. Currently, 2 9s and one are in
> > use, with /home wholly using one of the 9s. This means we have 4x 9gig
> > disks available for /home. There are several options:
> 
> Great!
> 
> We could still do with a SCA SBB to replace that 4 with a 9...
> 
> > o Software RAID 5 across all 4 disks. Gives 27gig usable space, some
> >   redundancy, some CPU hit.
> 
> Not just a CPU hit, a significant write performance hit. I wouldn't
> worry if it was /services, but I don't think that's best for /home.
> 
> Worse, it binds all those disks into one big clump that it's hard to
> grow/shrink/fiddle with, without having the same space again spare.
> 
> > o Two RAID 0 sets containing 2 disks each, added to the one domain. Gives
> >   36gig usable space, no redundancy, good performance, little CPU usage.
> 
> Ummm. Well. It's what we've lived with up until now, but you just can't
> trust disks these days, and these aren't even new disks...

We've been damned lucky. Similar Seagate 9Gbs fail all the time at UCS
and we have an air conditioned machine room. I'd say go the 2 * RAID-1
disk sets. Seems like the best option.

> I think that leaves us a prudent but high-performance choice of:
> > o Two RAID 1 sets containing 2 disks each, added to the one domain. Gives
> >   18gig usable space, good redundancy, little CPU usage (comparatively).
> [...]
> 
> We can also turn mirroring on and off, so we can copy the files from
> one set to the other and remove any fragmentation.

You shouldn't need to. If there is free space then the fragmentation
should be automatically kept down.