iostat

iostat -d or iostat -d 1 3 (intervals)

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn

emcpowerb         0.77         4.00         1.83    6815372    3116833

emcpowerb1        0.77         3.99         1.83    6806059    3116833

emcpowerc         0.79         4.12         1.86    7014439    3176798

emcpowerc1        0.79         4.11         1.86    7005126    3176798

emcpowerd         2.92       228.21        10.54  388964607   17958990

emcpowerd1        2.92       228.19        10.54  388930745   17958990

emcpowere         9.81       435.92        28.25  742987674   48147159

emcpowere1        9.81       435.90        28.25  742953820   48147159

tps:  transfers per second.  This is the nubmer of reads , writes to the partition per second
blk_read/s:  The rate of disk block read per second
blk_wrtn/s:  The rate of disk blocks writes per second
blk_read:  total number of block read
blk_wrtn:  total number of block writes

iostat Extended Statistics: can be useful to identify a particular disk as a bottle neck

rrqm/s :  numbers of reads merged
wrqm/s:  numbers of write merge
r/s:  number of reads issued to disk / second
w/s:  number of writes issued to disk /second
rsec/s:  Disk sectors read / second
wsec/s:  Disk sectors write/second
rkB/s:  KB reads from disk / second
wKB/s : KB write from disk / second
avgrq-sz : average size of disk request
avgqu-sz : average size of disk request queue
await:  avg time (in ms) for a request to be completed service
svctm:  avg time (in ms) for requests submmited to disk.  This indicates how long on average the disk took to complete a request.

iostat -x -dk 1 5 emcpowerb1Device:              rrqm/s   wrqm/s   r/s    w/s     rkB/s    wkB/s  avgrq-sz  avgqu-sz   await  svctm  %util
emcpowerb1        0.00     0.00   0.02   0.76     2.00     0.91     7.52      0.00         5.38   5.26   0.41