Not enough description to answer the question.

ESS is a disk subsystem.

Are you comparing it to EMC disk or to Connectrix.

I do not know if you can hook a ESS to a Connectrix.  I know they were
supposed to go open with Connectrix, but have not looked lately.

As far as SAN TDPs there are some current combination restrictions that are
supposed to all be lifted with V5.1.

TDP for SAP R/3 and Oracle support the following combinations of Timefinder
and FlashCopy:

ESS and AIX (FlashCopy)
EMC Symmetrix and Solaris (TimeFinder)

But not EMC Symmetrix/AIX and ESS/Solaris

Netbackup only supports EMC/Symmetrix.