tps for block device vs lvm device

[unlisted <unlisted@gmail.com>]

Why would I see 50x the amount of transactions on the lvm volume vs the actual underlying block device ?

 

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.00    0.00   11.41   57.07    0.00   31.51

Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
sda             211.33         0.00        56.12          0        113
sdb             268.47        63.05         0.00        128          0
dm-0          14365.52         0.00        56.11          0        113
dm-1              0.00         0.00         0.00          0          0
sdc               0.00         0.00         0.00          0          0

211 tps versus 14365 tps.  The box is idle and the following command was running:

 

dd if=/dev/sdb of=/home/xxxxxxx/bigrandomfile.txt bs=4k count=10000000

Sam

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