Messages in this thread | | | Date | Thu, 5 Feb 2004 16:23:04 +0100 (MET) | From | Mattias Wadenstein <> | Subject | Performance issue with 2.6 md raid0 |
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Greetings.
While testing a file server to store a couple of TB in resonably large files (>1G), I noticed an odd performance behaviour with the md raid0 in a pristine 2.6.2 kernel as compared to a 2.4.24 kernel.
When striping two md raid5:s, instead of going from about 160-200MB/s for a single raid5 to 300M/s for the raid0 in 2.4.24, the 2.6.2 kernel gave 135M/s in single stream read performance.
The setup: 2 x 2.0 GHz Opteron 248, 4 gigs of ram (running 32-bit kernels) 2 x 8-port 3ware sata raid cards, acting as disk controllers (no hw raid) 16 x Maxtor 250-gig 7k2 rpm sata drives. 1 x system drive on onboard pata doing pretty much nothing.
The sata drives are configured in 2 8-disk md raid5s, not hw raid for performance reasons, we get better numbers from the md driver in that case than the hw raid on the card. Then I have created a raid0 of these two raid5 devices.
I used jfs for these numbers, I have only seen minor differences in speed in the single-stream case on this hardware though for different filesystems I have tested (ext2, xfs, jfs, reiserfs). And the filesystem numbers are reflected pretty close by doing a dd from /dev/md10. The same goes for increasing the chunk-size to 4M instead of 32k, roughly the same numbers. The system is not doing anything else.
The results (as meassured by bonnie++ -f -n0, all numbers in kB/s, all numbers for a single stream[*]): 2.4.24, one of the raid5s: Write: 138273, Read: 212474 2.4.24, raid0 of two raid5s: Write: 215827, Read: 303388 2.6.2, one of the raid5s: Write: 159271, Read: 161327 2.6.2, raid0 of two raid5s: Write: 280691, Read: 134622
It is the last read value that really stands out.
Any ideas? Anything I should try? More info wanted?
Please Cc: me as I'm not a subscriber to this list.
[*]: For multiple streams, say a dozen or so readers, the aggregate performance on the 2.6.2 raid0 went down to about 60MB/s, which is a bit of a real performance problem for the intended use, I'd like to at least saturate a single gigE interface and hopefully two with that many readers.
/Mattias Wadenstein - 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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