node9:~ # lsscsi 

[0:0:0:0]    disk    ATA      INTEL SSDSC2BW18 DC12  /dev/sda 
[1:0:0:0]    disk    ATA      INTEL SSDSC2BW18 DC12  /dev/sdb 
[2:0:0:0]    disk    ATA      WDC WD5000HHTZ-0 04.0  /dev/sdc 
[3:0:0:0]    disk    ATA      WDC WD5000HHTZ-0 04.0  /dev/sdd 
[4:0:0:0]    disk    ATA      WDC WD5000HHTZ-0 04.0  /dev/sde 
[5:0:0:0]    disk    ATA      WDC WD5000HHTZ-0 04.0  /dev/sdf 

node9:~ # sync;echo 3 > /proc/sys/vm/drop_caches;dd if=/dev/sdf of=/dev/null

bs=1024k count=4096
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 23.7882 s, 181 MB/s

node9:~ # sync;echo 3 > /proc/sys/vm/drop_caches;dd if=/dev/sda of=/dev/null

bs=1024k count=4096
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 8.05345 s, 533 MB/s