I am having performance issues with my LTO4 tape drives in my Comm Vault environment. I have a Windows VCB proxy server running Windows 2003 server Ent Edition. We are running Comm Vault Simpana 8 as our Ent backup software. There are 2 Emulex HBAs in the proxy server one zoned to the tape drive SAN and the other zoned to the storage SAN. The majority of our ESX environment is ESX v 3.5 so we still need to use VCB. I am seeing on average 1260mb/min when writting to our LTO4 tape drives which if I calculated correctly is roughly 17% of its potential through put. Is anyone else running this configuration and if so what are you seeing for performance? The tape library is an IBM TS3500 with LTO4 tape drives. We have on board encryption running and we are using TKLM as our key management software.