[mythtvnz] File System for RAID-5

[David Zanetti]

On Thu, 2009-06-18 at 12:57 +1200, James Booth wrote:
> Thanks Steve. RAID1 with LVM will give me what I need, I was just
> hoping for RAID 1+0 so I could also get the performance gain, which
> may be handy if I end up with three frontends all watching and
> recording HD at the same time.

For read streams, software RAID-1 will scatter the workload over both
disks. So if you have a few front-ends reading, it won't actually be
single-disk performance.

Write in *all* RAID modes has a penalty, it's a fair bit lighter in 1
than 5 purely because 1 involves writing to less disks to update a
block.

My preferred approach is RAID-1 pairs with LVM spanning the whole set.
This gives me good reliability without too much loss in performance, and
an easy migration path to more storage, thanks to various uses of
degraded array modes. 

RAID-5 only makes sense if you are seriously strapped for cash or
physical space to put disks. Otherwise, the write performance is slower,
the failure cases are a bit more hairy, and expansion is even hairier.

Go with simple disk systems, people! I've lost enough over the years to
pushing my luck, and you really want simple arrangements.

-- 
David Zanetti <dave2 at wetstring.net>
http://hairy.geek.nz/