[mythtv-users] LVM RAID 5 partition schemes

[Dan Christensen]

Milan Andric <mandric at gmail.com> writes:

> I'm planning on sqeezing as much as I can into a microATX case
> to make my mythtv frontend/backend. I also want to make this
> a media storage box/file server, ie. include a RAID 5 LVM storage setup.
>
> I'm basically stuck on the RAID.  Since I  do not have enough data
> *right now* to use the 3 x 300G RAID 5,  I'd like to just buy two
> drives now and use mdadmin to
> setup a RAID 5 with 2 missing drives and add drives as time goes on.

2 missing drives, or 1?  I assume you meant 1.

> I know it's required to have 3 drives to make a RAID 5 array.  But is
> there a way to fake so I can add a third drive later?  Or do I just
> have to fork up the cash now?

I'm pretty sure you can install things with one drive missing, but
then you have no redundancy in the meantime.  Alternatively, you could
set up RAID-1 (mirroring) for now, and migrate to RAID-5 later.  There
is a tool to do this without a backup (see the Software RAID Howto),
but it might be risky.

I think you're better off just buying the 3 drives now.  It'll
save a lot of headaches.

> If you could post your partition scheme or how you setup 
> your partitions/drives it would help me.

One thing I did which I hadn't heard of before is to split each
drive in half, and make two RAID-5 arrays, one consisting of the
first half of each drive, and one consisting of the second half
of each drive.  Then I use lvm to make a big partition using
both RAID-5 arrays.  The reason I did this is that I have an
external drive just large enough to back up each of these
RAID-5 arrays (but not both), so if I ever want to add an
extra drive, I'll be able to expand one RAID array at a time,
with a backup for safety.

> Has anyone tried to mix/match devices like ATA and SATA to create a
> raid 5 with md?

I haven't tried it, but it should work.  md accepts any block
device; you can even layer RAID over RAID.

Dan