[mythtvnz] Myth & Raid. SW or HW..

[Steve Hodge]

On Thu, Jul 19, 2012 at 8:57 AM, Toby Mills <millst at np.co.nz> wrote:

> >Many seem to take the view that there is little point to RAID since
> primary
> >storage is for TV recordings, which I agree are low value. However, in my
> case
> >the bulk of my data is not taken up with TV recordings but movies and
> music,
> >which I consider very high value since I don't know how many hours of
> labour I >put in ripping my rather huge DVD and CD collection.
>
> This is a good point about videos and music, its wise to remember that
> RAID is not a backup strategy.
> RAID is a method of avoiding downtime and increasing performance, however
> in a myth setup, there is a relatively low cost of downtime so RAID has a
> lower value.
>
> I take the same view on Videos and Music, however I don't safeguard this
> with RAID.
> I simply use the same 1Tb USB drive that I use for configuration backups
> as my primary storage of Videos and music, but then use RSYNC to take a
> weekly copy of this onto another 1Tb USB drive.
>

That's a good strategy for 1TB, but I've got about 4TB of movies and music
and other stuff. That means I'd have to manage about 2 or 3 backup drives.
If I'm buying 2 or 3 more drives then I'd rather have that capacity
available. RAID makes sense for me - it combines the capacity of the disks
which reduces messing around moving things to make them fit, it increases
performance, and it provides a level of fault tolerance. I have a backup -
the original DVDs and CDs - but it'd be a lot of work to recover from that
backup.


> The key issue with RAID for mythtv is fragmentation, fragmentation can
> offset the increased perofmance you get from having raid.
>

What are you doing with Myth that needs so much performance? I'm running
Myth on a single drive - OS, database, and recordings. I can record 3 or 4
things, commflag, and watch at the same time. Admittedly I'm still SD only
at the moment, but still. I should have the same fragmentation issues as a
RAID array would have, yet I've never had any problems. I've never really
noticed anyone having IO performance issues on the mailing lists either.

If you used the same disks in your raid array to create 1 storage group
> from each disk then your performance will be better than any RAID
> configuration and your risk of data loss will be lower than every single
> raid configuration except RAID 10.
>

This is not true. With storage groups you will lose data with a single disk
failure. You just won't lose all of it. With any RAID (expect RAID 0) you
will not lose anything to a single failure.

All that said, I agree that storage groups are the way to go for recordings.

Cheers,
Steve
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ourshack.com/pipermail/mythtvnz/attachments/20120719/87ff9142/attachment.html>