Hi,

   What command did you use to create your raid-10?  You might try  
running iostat in parallel to see if the read_balancer is properly  
balancing the reads between the two disks.

   I've seen situations where raid-10 on sequential reads will pretty  
much always prefer the same disk and barely use the mirror.

   One thing we looked at was changing to the far layout, which helped  
a bit.

--Rob
On Oct 16, 2009, at 10:32 AM, adfas asd wrote:

I was hoping to get better performance with RAID10 than from the raw  
disks, but that's turned out to not be the case.  Experimenting with  
the readahead buffer I get these bandwidths with the following  
command:
# time dd if={somelarge}.iso of=/dev/null bs={readahead size}

/dev/sd?
1024 71.3 MB/s
2048 71.2 MB/s
4096 77.7 MB/s
8192 69.4 MB/s
16384 76.6 MB/s

/dev/md2
1024  67.1
2048  69.1
4096  75.7
8192  64.9
16384 69.0

Using RAID10offset2 on 2 WD 2TB drives, and always the same input  
file.

Why would RAID10 performance be -poorer-?
If it weren't for mirroring, this wouldn't be worth it.






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