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I've got software raid 1 for / and /home and it seems I'm not getting the right speed out of it.

Reading from md0 I get around 100 MB/sec Reading from sda or sdb I get around 95-105 MB/sec

I thought I would get more speed (while reading data) from two drives. I don't know what is the problem.

I'm using kernel 2.6.31-18

hdparm -tT /dev/md0

/dev/md0: Timing cached reads: 2078 MB in 2.00 seconds = 1039.72 MB/sec Timing buffered disk reads: 304 MB in 3.01 seconds = 100.96 MB/sec

hdparm -tT /dev/sda

/dev/sda: Timing cached reads: 2084 MB in 2.00 seconds = 1041.93 MB/sec Timing buffered disk reads: 316 MB in 3.02 seconds = 104.77 MB/sec

hdparm -tT /dev/sdb

/dev/sdb: Timing cached reads: 2150 MB in 2.00 seconds = 1075.94 MB/sec Timing buffered disk reads: 302 MB in 3.01 seconds = 100.47 MB/sec

Edit: Raid 1

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what kind of raid? – hop Jul 7 '10 at 16:40
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2 Answers

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Take a look at the following article at nixCraf, HowTo: Speed Up Linux Software Raid Building And Re-syncing.

It explains the different settings in /proc that can be adjusted to influence the software raid speed. (Not just during building/syncing as the title suggests.)

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Thanks! Using these settings I get at least 10% more speed while doing sequential reads. – Jure1873 Jul 7 '10 at 16:59
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up vote 1 down vote

What kind of RAID?

Any combination of 0 and 1 will give no great improvement to a non-concurrent benchmarks for latency or bandwidth. RAID 3/5 should give better bandwidth but no difference in latency.

C.

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sorry I forgot to specify it's Raid1. I was under the impression that raid 1 should give at least 20% more speed because it can read from both drives in parallel. – Jure1873 Jul 7 '10 at 16:46
If it were hardware raid then it may be able to optimize seeks much more effectively than software raid. That's not to say that its impossible with software raid - but it'd need to be very smart, and it would only really be of benefit for machines running small numbers of tasks concurrently. I expect you would see a difference if you were running two (or more instances) of the benchmark concurrently (it'd probably show slower stats than running one at a time - but not twice as slow). – symcbean Jul 8 '10 at 14:24
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