[mythtv-users] Raid 5 Performance Tweaking

Dean Wilson dean.k.wilson at gmail.com
Mon Jun 5 17:15:02 UTC 2006

I recently installed Fedora Core 5 from scratch on a raid5 array of 5
disks.  But I didn't see any options for how to configure the raid
array, and now I'm wondering if it could be tweaked better for large
files (i.e. for use with myth)  I read in the wiki
(http://www.mythtv.org/wiki/index.php/RAID, and
http://www.tldp.org/HOWTO/Software-RAID-HOWTO-9.html) that a 32K chunk
size and 4K block size was the best setup.  However, I notice that
when I run 'cat /proc/mdstat' I get the following:

     Personalities : [raid5] [raid4]
     md0 : active raid5 sdd1[4] sdc1[3] sdb1[2] sda1[1] hda3[0]
           976783360 blocks level 5, 256k chunk, algorithm 2 [5/5] [UUUUU]

Apparently the default setup for FC5 was 256k chunks.  (Which doesn't
state block size -- anyone know how to find that?)  I noticed that the
raid performance page doesn't test beyond 32K chunk sizes -- does
anyone know which is best?  (I would think that larger chunk sizes are
better for large files, but I don't know...)

Also, I found the Raid Howto
(http://www.tldp.org/HOWTO/Software-RAID-HOWTO-5.html) which states
that "RAID-{4,5} performance is severely influenced by" stride
settings for mke2fs.  Since I'm using xfs, is there a similar setting
I should use?

(I guess I should also ask if it's possible to change these settings
at this point?  If not, would the performance gain be worth

Thanks in advance,

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