[mythtv-users] RAID suggestions?

Sean Goodpasture goofygrin at gmail.com
Thu Oct 25 15:52:24 UTC 2007


Been running a software raid 5 for a few years (PATA even) with little
issues.  Using hdparm for speed tests helped me to tweak the stripe size and
such.  IIRC, it was about 3-4 times faster reading from the raid than from a
single disk.

I don't write myth recordings to it, I use unRaid for my myth recordings.
Check it out, it's free for just three drives, but you'll require another
computer.


On 10/25/07, Patrick Wagstrom <patrick at wagstrom.net> wrote:
>
> Greg Arena wrote:
> >       I just recently bought a trio of 500 GB SATA hard disks
> > that I want to put together in a RAID 5 configuration for my
> > MythTV box. These will only be used for storing recordings &
> > videos - I have an 80GB PATA drive in place that I'll keep there
> > for the OS, MythTV software, logs, etc. I plan to use Linux's
> > software RAID support - true hardware RAID was just too
> > expensive.
> >       I've heard mixed reports about using RAID 5 for media
> > stuff. The MythTV wiki doesn't recommend it without expensive
> > hardware RAID controllers, but yet I've heard people talking
> > about their RAID 5 setups on this list and elsewhere. I was
> > wondering if anybody has gotten something similar working and
> > what settings they used (stripe size, etc.) since I've never set
> > up a RAID before. I've already run some benchmarks using bonnie++
> > with one drive by itself to use for comparison after setting up
> > the RAID to try to make sure it's not going to degrade
> > performance excessively. I'm willing to spring for another hard
> > disk to go to a four-disk RAID 10 configuration if RAID 5 looks
> > like it'll be too slow.
>
> I'm not an expert on raid or filesystems by any extent, but I've had no
> problems over the past two years running a 4x320GB SATA2 RAID5 array
> with XFS on it.  The actual amount of disk IO that MythTV needs to do is
> pretty small, a couple of megabytes a second at most.  I've tested this
> with 3 HD and an SD recording with HD playback going on at the same time
> on an Athlon 64x2 4400+ with no problems.
>
> Performance wise, here's a comparision of block performance from Bonnie++:
>
> IDE drive: Output 49971K/s, Input 50581K/s
> SATA raid: Output 43444K/s, Input 154578K/s
>
> So yeah, it's a little slower for writes, but it's nice and fast for
> reads.  In any case, 43MB/s is fast enough for lots of HD streams.  When
> you have parallel readers/writers, the issue gets a little worse, but
> you still have enough overhead there for seek issues...which you'd have
> on RAID10 anyway.
>
> >       I'm also considering using XFS for the file system for
> > storing all the media files on this RAID. Any suggestions on how
> > to optimize it for RAID 5 or RAID 10? I've never used anything
> > but ext3 for my Linux boxes until now, so I'm new to XFS as well.
>
> XFS is a good choice.  For Myth folks, one of the big advantages is that
> it's extents based, so deletes are pretty fast.
>
> --Patrick
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