Re: Linux Software RAID5 - ballpark numbers

In article <jq-dnXohqbu8Ll3YnZ2dnUVZ8v3inZ2d@xxxxxxxxx>,
Rohan Beckles <rohan.beckles@xxxxxxxxxx> wrote:

OK, an addendum - I just done a unbuffered write of the same 4.4GB DVD ISO
onto the 7-drive RAID0 array - average write was 25MB/s. How does this
work? (I will post unbuffered RAID5 results as soon as possible).

Second question is this: is the selection of optimal chunk size for RAID 5
based on N drives or N - 1 drives? In other words, is the parity data
subject to the same chunk distribution as the non-parity data?

Again, many thanks for help and advice,

I can't give you other advice but to use only disks of exact same model.
I have few servers running debian (testing) with software RAID 5 : 3 HD
RAID5 + 1 HD Spare. HD are 36 GB Raptor SATA 2. Here are the benches:

no RAID:

# hdparm -t /dev/sdd1
/dev/sdd1:
Timing buffered disk reads: 208 MB in 3.01 seconds = 69.08 MB/sec

# bonnie++ -d /var/tmp/ -m debian-sdd1 -n 2:2000000:10000:20 -u patpro
debian-sdd1,16G,63105,71,69012,14,27908,3,45015,45,44610,2,195.3,0,2:2000
000:10000/20,529,92,2235,100,61,1,598,99,2224,99,60,1

3 HD RAID 5:

# hdparm -t /dev/md0
/dev/md0:
Timing buffered disk reads: 414 MB in 3.00 seconds = 138.00 MB/sec

# bonnie++ -d /raidroot/tmp/ -m debian-md0 -n 2:2000000:10000:20 -u
patpro
debian-md0,16G,90003,92,86674,16,22231,6,58731,59,71847,8,291.9,0,2:20000
00:10000/20,1018,96,1884,99,201,3,1201,99,2337,99,2600,48


this is really out of the box performance, no tuning at all.

patpro

--
http://www.patpro.net/
.

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