Messages in this thread | | | Date | Sat, 8 May 2004 14:51:39 +0200 | From | Marc Lehmann <> | Subject | unexplainable low ide raid performance, slower than a single raid disk |
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Hi,
I've got a lvm-on-raid-on-ide setup, with 5 IDE disks, all on their own channel.
However, neither read nor write speed is as high as one would expect.
Every single disk is capable of delivering roughly 50MB/s (measured with hdparm -tT), except one, which only does 46MB/s (it's only 5400rpm):
/dev/hdk: Timing buffer-cache reads: 812 MB in 2.01 seconds = 404.65 MB/sec Timing buffered disk reads: 158 MB in 3.03 seconds = 52.17 MB/sec
When I do dd if=/dev/somedisk of=/dev/null bs=1024x1024 on two disks, I get ~62MB/s and three disks deliver about 68MB/s, which seems to be the maximum this (slightly older) system can deliver.
The reconstruction speed I get on an idle system is ~13500kb/s, which, with five disks, corresponds nicely with the 68MB/s my system is capable of delivering.
So all this is relatively consistent.
However, the raid device itself is much slower, never ever reaching the speed of even a _single_ disk:
/dev/hdk: Timing buffer-cache reads: 812 MB in 2.00 seconds = 405.25 MB/sec Timing buffered disk reads: 128 MB in 3.02 seconds = 42.32 MB/sec
Wether hdparm or reading/writing with dd, the linera throughput on the raid device is always much lower, and I have no idea why this is the case, and I wonder wether this is a problem with my setup and wether it can be fixed.
Here is some more info about my system that might or might not be useful:
* Dual-PIII 1Ghz * kernels 2.6.4 and 2.6.5 consistently show this behaviour. * one disk is on the secondary via vt82c686 controller, * all other disks are on promise 20268 devices, all ATA 100 controllers. * the raid was clean (non-degraded) during all my tests, and I have re-run them a few times on an otherwise idle system and got about the same figures. * 1 x SAMSUNG SV1604N, 4 x SAMSUNG SP1604N drives * md0 : active raid5 hdk1[3] hdi1[2] hdg1[1] hde1[0] hdc1[4] 625163264 blocks level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]
Thanks a lot for any insights or ideas on this problem.
-- -----==- | ----==-- _ | ---==---(_)__ __ ____ __ Marc Lehmann +-- --==---/ / _ \/ // /\ \/ / pcg@goof.com |e| -=====/_/_//_/\_,_/ /_/\_\ XX11-RIPE --+ The choice of a GNU generation | | - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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