Interpreting these iostat results

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Hi,

    As a result of running this command, 'iostat -x -m 30 30'. I get the following output. sda and sdb are sata3 drives in a striped raid (0).

    How do I interpret these results for a raid. Specifically,
    a) await to svctm ratio is close to 1 for individual drives but > 2 for dm-x.
    b) I expected to see rMB/s closer to 300 which is the SATA3 speed with the reasonable good disks I am using. But these are at 1.xx MB/s. What does thie mean?
    c) What's the interpretation to monitor the raid performance? Seems like there is enough bandwidth for I/O here but when I bump up the processes just a notched, there is a long await to svctm ratio.

Thanks,
Madhav.

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          33.62    0.00    6.90    0.02    0.00   59.45

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await  svctm  %util
sda              10.03     0.20   20.37    0.20     1.16     0.00   115.19     0.05    2.63   2.53   5.21
sdb              10.07     0.00   19.97    0.13     1.15     0.00   117.67     0.05    2.65   2.56   5.14
dm-0              0.00     0.00   41.93    0.47     2.31     0.00   111.60     0.12    2.88   1.35   5.70
dm-1              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
dm-2              0.00     0.00   41.93    0.47     2.31     0.00   111.60     0.12    2.88   1.35   5.71
dm-3              0.00     0.00   41.93    0.40     2.31     0.00   111.77     0.12    2.89   1.35   5.71
dm-4              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00

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