[mythtv-users] Software RAID5 faster than RAID10?

[Ben Curtis]

Well, unless I'm doing something really wrong in my testing, I've just
learned that my Software RAID5 is faster at reading and writing than my
Software RAID10.  Please disprove this if at all possible, as I'm sure this
will be useful information for anyone setting up a new filesystem for their
video or system partitions.  Looks like I may be converting my RAID10 to a
RAID5.  If there are other methodologies I should use to test, let me know
and I'll be happy to post the results.

Tested on Fedora Core 10, using 4 500GB drives, split up into multiple
partitions.  Repeated testing showed pretty much the same results. 
HOWEVER, testing write speeds with a larger file changed the results,
causing the results to be closer together.

---------------------------------------------------
Structure: 4 partitions for a 50GB RAID10 (md2)
Mounted on: /
--------
[root at tvserver ~]# date; dd bs=1G if=/dev/zero of=tmp.img count=1; date; rm
tmp.img
Mon Apr 13 15:39:19 EDT 2009
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 6.73574 s, 159 MB/s
--------
[root at tvserver ~]# date; dd bs=3G if=/dev/zero of=tmp.img count=1; date; rm
tmp.img
Mon Apr 13 15:46:27 EDT 2009
0+1 records in
0+1 records out
2147479552 bytes (2.1 GB) copied, 16.1687 s, 133 MB/s
Mon Apr 13 15:46:45 EDT 2009
--------
[root at tvserver ~]# hdparm -tT /dev/md2
/dev/md2:
 Timing cached reads:   5564 MB in  2.00 seconds = 2784.46 MB/sec
 Timing buffered disk reads:  450 MB in  3.01 seconds = 149.60 MB/sec
---------------------------------------------------

---------------------------------------------------
Structure: 4 partitions for the rest of the space in RAID5. (md3)
Mounted on: /files
--------
[root at tvserver files]# date; dd bs=1G if=/dev/zero of=tmp.img count=1;
date; rm tmp.img
Mon Apr 13 15:35:17 EDT 2009
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 4.90092 s, 219 MB/s
--------
[root at tvserver files]# date; dd bs=3G if=/dev/zero of=tmp.img count=1;
date; rm tmp.img
Mon Apr 13 15:46:00 EDT 2009
0+1 records in
0+1 records out
2147479552 bytes (2.1 GB) copied, 15.3082 s, 140 MB/s
Mon Apr 13 15:46:15 EDT 2009
--------
[root at tvserver ~]# hdparm -tT /dev/md3
/dev/md3:
 Timing cached reads:   5360 MB in  2.00 seconds = 2682.82 MB/sec
 Timing buffered disk reads:  640 MB in  3.00 seconds = 213.17 MB/sec
---------------------------------------------------