[mythtv-users] recommendations for building new FE/BE HDTV system?

[Brian Wood]

On Sunday 05 April 2009 12:31:19 David Brodbeck wrote:
> Tyler T wrote:
> > That's basically what I've done with some old PATA drives. 16GB Raid-1
> > for the OS, then a second partition on the first drive for NAS --
> > which is backed up nightly to a sister partition on the second disk
> > (because Raid-1 is NOT a backup!). Then the rest of each drive is
> > Raid-0 for recordings. Works great, although you do take a small hit
> > on the extra power consumption.
>
> Why are you using RAID 0 instead of Storage Groups?  (This isn't a
> criticism, I'm genuinely curious.)  I would think Storage Groups would
> be a bit more reliable -- losing one drive would take out half your
> recordings, instead of all of them.

One word: Performance.

I don't mean to answer for the person to whom the question was directed, but I 
can tell you why I use RAID0 instead of Storage Groups.

RAID0 will increase the performance of the disk system, while Storage Groups 
(or LVM) will not. Note this example (sda is a single drive, md1 is a 
two-drive RAID0 array:

/dev/sda:
 Timing cached reads:   1822 MB in  2.00 seconds = 911.75 MB/sec
 Timing buffered disk reads:  174 MB in  3.00 seconds =  57.98 MB/sec

/dev/md1:
 Timing cached reads:   1798 MB in  2.00 seconds = 899.41 MB/sec
 Timing buffered disk reads:  522 MB in  3.00 seconds = 173.98 MB/sec


I'm not sure why the RAID array is more than twice as fast as the single 
drive, but it appears to be, at least according to this somewhat limited 
test.

I understand that using the 2 drives in RAID0 doubles my chances of losing 
data to a drive failure, and that a single drive failing will cost me ALL the 
data on the array, but I'm willing to put up with that. The array is backed 
up regularly, and I like the performance bump.

In fact, with most Myth systems, a single drive is fast enough, but the 
improvement is real and significant.

-- 
beww
beww at beww.org