[mythtv-users] Disk Arrangement and LVM + JFS

[John Drescher]

>   I've also found that the software raid5 was noticably slower on my setup
> (even with an Athlon 64 X2 4800+ and 2GB DDR2 800 DC ram) - perhaps that's
> because I have 5 tuners and have very little 'idle' time -- sometimes even
> all 5 tuners recording at once.
>
The biggest problem is mythtv's builtin sync writing mechanism is very
bad for a raid5 or 6 array. I mean it forces a lot of small writes
which is very bad for raid5/6 because if you write smaller than the
stripe size and the whole stripe is not in the cache the os has to
read the entire stripe from disk inorder to write. Increasing the
default stripe cache size can be a huge benefit here.

something like (for md1):

echo 2048 > /sys/block/md1/md/stripe_cache_size

to see if the stripe cache is being overrun check the
 /sys/block/md1/md/stripe_cache_active

and see if it is being maxed out.

John