[mythtv-users] Storage Questions. LVM, RAID, NFS

[Dean Wilson]

I'm considering increasing the number of drives I'm using.  When I do
that, I would like to go to a redundant system for reliability. 
Unfortunately, I've never used raid before, and would like some input.

Because of the size required for HD TV as well as space required for
mail and web server files, I'm aiming for ~1TB of usable storage
space, which would be prohibitively expensive to double the disks. 
That said, what are my best options?

I've noticed that mwadm supports Raid 0, 1, 4, 5, 6

Raid 0 has no redundancy, so it isn't preferred
Raid 1is redundant, but requires too many disks (correct?)
Raid 4 ?
Raid 5 has redundancy (correct?), but I've heard that it writes very
slowly.  Would a Raid5 system be too slow for recording 2 HD + 1 SD
recording, while doing playback to up to two frontends at the same
time?
Raid 6 ?

As I understand it from these discussions, Raid5 requires 5 drives, 4
of which will be used for storage?  (So 5 250GB drives would sum to
1TB of useable HD space?)

Also, (assuming all raid configurations require more than 4 drives to
affordably hit my 1TB target with redundancy) I have a motherboard
that has 4 SATA ports, but with two different controllers, I'll still
need an SATA card for the 5th+ drive(s) (unless mdadm can mix IDE with
SATA?  Is this just asking for trouble?)  Will multiple controllers
adversely affect the raid array?  (If so, is there a controller card
anyone would recommend with 5+ SATA ports?)

Thanks for your help!

On 4/28/06, chris at cpr.homelinux.net <chris at cpr.homelinux.net> wrote:
> On Thu, Apr 27, 2006 at 10:26:15PM -0400, Thom Paine wrote:
> > So if I have 5 80G drives, I could rotate them out one at a time for
> > 320G drives? So long as I always have 5 drives in the array I'm good
> > to go?
>
> Yes.  As long as you are using the mdadm package.  Partition the new
> drives with auto-raid partitions and swap them in one at a time.  When
> you hot-add the drive, the 320G partition will receive a rebuild of the
> 80G partition it was replacing.  Once all 5 drives are running at 80G,
> you use the mdadm program to "grow" the array and it will expand to the
> size of the smallest partition in the array (which will all be 320G
> now).  Then resize your filesystem using whatever tool is appropriate
> for that filesystem.  Voila - 1.2T of storage, and the machine never
> even needed to power down (if you have hot-swappable drives).
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>