[mythtvnz] File System for RAID-5

[Tim Gibson]

I don't think with any RAID setup you can add another drive unless it's the
same size as the others in the array, so extending a RAID setup can/could be
difficult, you could easily have a RAID1 array with two 1TB drives and a LVM
on top then make another RAID1 array with another two, say, 2TB drives and
extend the LVM across the two RAID1 setup's.  Also unless you want a real
performance hit I'd shy away from splitting your 1TB drive into 2 500G
partitions and adding them into the same RAID array as the data would then
be written to the same physical drive twice.

p.s I'm now running ext4 on my main storage drive, so far no problems...
touch wood.

Tim

2009/6/18 Stephen Worthington <stephen_agent at jsw.gen.nz>

> 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:
> >
> >>  Thanks Steve. RAID1 with LVM will give me what I need, I was just
> hoping
> >> for RAID 1+0 so I could also get the performance gain, which may be
> handy if
> >> I end up with three frontends all watching and recording HD at the same
> >> time. If I had three RAID1 arrays as per Tim’s email, and then put RAID0
> >> over the top, could I subsequently add in another RAID1 pair as per
> Tim’s
> >> directions, and then grow the RAID0 across the extra RAID1 pair without
> >> having to backup? I guess in short I’m asking can you currently add
> >> disks/partitions to a RAID0 automatically without loss of data? I find
> many
> >> conflicting answers on the net.
> >>
> >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.  The
> Linux caching algorithms are good, and will reduce the head movement a
> lot, but there will still have to be head movement.  And while the
> read and write speeds for modern 7200 rpm SATA drives are quite
> staggeringly big, the stepping rates have not changed in ages and are
> still a *lot* slower than even quite old 10k or 15k SCSI drives.
>
> That said, my two Seagate 7200.10 500 Gibyte data drives combined as
> one LVM/JFS partition cope well with the above scenario, but only at
> MPEG data rates from my PVR-500 tuners.  I have yet to move my DVB-T
> tuners onto the Myth box to find out if they will work as well when
> there are two 1080i and two 720p programs being recorded at the same
> time.
>
> >As far as I know you can't extend RAID0 arrays with mdadm either (at least
> >the man page says 1/4/5/6 only). My advice is that if you're really
> >expecting to extend the array any time soon just buy the drive now.
> >
> >By the way, that stuff you keep referring to from Tim's email was also
> >written by me :-)
> >
> >Cheers,
> >Steve
>
> _______________________________________________
> mythtvnz mailing list
> mythtvnz at lists.linuxnut.co.nz
> http://lists.ourshack.com/mailman/listinfo/mythtvnz
> Archives http://www.gossamer-threads.com/lists/mythtv/mythtvnz/
>



-- 
Regards
Tim, Donna and Erin Gibson
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.ourshack.com/pipermail/mythtvnz/attachments/20090618/23ed373a/attachment-0001.htm