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Subjectraid0 slower than devices it is assembled of?
Date
I've got / on linux-raid0 on 2.6.0-t11-cset-20031209_2107:
<cite>
/dev/md/1:
Version : 00.90.01
Creation Time : Thu Sep 11 22:04:54 2003
Raid Level : raid0
Array Size : 232315776 (221.55 GiB 237.89 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 1
Persistence : Superblock is persistent

Update Time : Mon Dec 15 12:55:48 2003
State : clean, no-errors
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Chunk Size : 64K

Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/sda3
1 8 19 1 active sync /dev/sdb3
UUID : b66633c2:ff11f60d:00119f8d:7bb9fc6c
Events : 0.357
</cite>
Disks are two ST3120026AS connected to sii3112a controller, driven by sata_sil
'patched' so no limit for block size is applied (it's not needed for it).

Those are results of hdparm -tT on drives:
<cite>
/dev/md/1:
Timing buffer-cache reads: 128 MB in 0.40 seconds =323.28 MB/sec
Timing buffered disk reads: 64 MB in 1.75 seconds = 36.47 MB/sec
/dev/sda:
Timing buffer-cache reads: 128 MB in 0.41 seconds =309.23 MB/sec
Timing buffered disk reads: 64 MB in 1.46 seconds = 43.87 MB/sec
/dev/sdb:
Timing buffer-cache reads: 128 MB in 0.41 seconds =315.32 MB/sec
Timing buffered disk reads: 64 MB in 1.23 seconds = 52.04 MB/sec
</cite>
What seems strange to me is that second drive is faster than first one
(devices are symmetrical, sd[a,b]2 is swapspace (not mounted at time of
test), sd[a,b]1 is /boot (raid1)).
What is even stranger is that raid0 which should be faster than single drive,
is pretty much slower- what's the reason of that?
--
Witold Kręcicki (adasi) adasi [at] culm.net
GPG key: 7AE20871
http://www.culm.net
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