[mythtv-users] RAID suggestions?

[Patrick Wagstrom]

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