[mythtv-users] Reassemble RAID with mdadm

[freedenizen]

On Wed, Mar 17, 2010 at 4:04 PM, MarcT <myrdhn at gmail.com> wrote:
> RAID 6 would be the best setup (4-2, similar to the 4 drive 10 or 0+1 setup
> but you can lose any 2 drives ant not 1 drive from each mirror/stripe)
> However, for software RAID, I don't think we are ready for that yet with
> today's systems and you would see the performance hit that was commented on
> above. You would need a hardware RAID controller to make use of RAID 6
> without seeing a significant hit to performance.

I'm not so sure about this, I mean we are talking about TV recordings,
even HD, which is pretty light IO wise.  I've seen quite good software
RAID 6 performance, and other people have as well:
http://louwrentius.blogspot.com/2009/06/linux-raid-6-performance-using-software.html

Even without making a massive array like that, your performance with
RAID6 will be more then good enough for your recording needs, and
being able to survive 2 disks failures is very nice, especially as you
end up increasing the size of the array (which happens to all of us).

One thing to note, mdadm 3.1 and kernel => 2.6.32 should support RAID
level modification, meaning you can move from one raid level to
another, it also support other online changes.  I wouldn't go for 3.1
yet myself, as it is still pretty fresh, and I'm sure there are bugs
to work it.  Also to note those features require superblock ver 1.1