[mythtvnz] File System for RAID-5

[Steve Hodge]

On Thu, Jun 18, 2009 at 5:45 PM, Stephen Worthington <
stephen_agent at jsw.gen.nz> wrote:

> On Thu, 18 Jun 2009 13:30:55 +1200, you wrote:
>
> >On Thu, Jun 18, 2009 at 12:57 PM, James Booth <james at booths.net.nz>
> wrote:
> >> I end up with three frontends all watching and recording HD at the same
> >> time.
> >>
> >I wouldn't worry too much about the performance - hard drives are at least
> >an order of magnitude faster than HD streams. I believe TV3 runs around
> >11Mbps, a modern drive will easily handle in excess of 400Mbps. A two disk
> >RAID1 should be capable of nearly twice the single disk read speed - when
> >you've got multiple reads going (as its the case with streaming three
> files
> >to different frontends) RAID1 should be approximately the same speed as
> >RAID0 for the same number of drives.
>
> You are missing the point a bit when you refer to disk speed only in
> Mbit/s.  That is a useful number only when the disk is being used for
> just one data stream.  If there are four tuners writing to the disk,
> another recorded program being played, and the four new recordings are
> being commercial scanned, then there are 9 data streams being used and
> the disk heads are going to have to be moving between them all.


You're right about this, but note that I was talking about reading only, as
was James. As I said RAID 0, 1, and 5 can all have pretty similar
performance (per disk) reading multiple streams. But if you've got 4 or more
recordings going at once you are probably much better off using separate
filesystems on separate disks with storage groups. If you're really worried
about losing recordings then set up a couple of separate RAID1s with storage
groups. That will probably perform better than a single RAID array of any
type.

Cheers,
Steve
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