dd command should be available in ESXi as well as all Linux versions. If you face any issues with your application and wants to know the disk performance is deteriorated, you can quickly use the dd command to check the write/read performance of the disk. The disk used can be even a datastore or a network device also. You can cross check with another system or disk where you don’t see any performance issues to compare the results to know if there is any issues with the disk.
Below is the example to run in a VMWare ESXi volume.
/vmfs/volumes/54a55c07-9face633-0999-002590fc98c8 # time dd if=/dev/zero of=test bs=1M count=1024
1024+0 records in 1024+0 records out
real 2m 7.62s user 0m 4.69s sys 0m 0.00s
= ( 1024/127 = 8 MB/s !!! )
In the above example you are trying to write a 1GB file and you are using time command to find out the speed at which the write happened.