Keeping this one alive. I'm also seeing this on an old MS cluster running exchange. It is interesting that many who've posted are seeing this on clusters. SRB stands for SCSI_Request_Block and is the responsibility of the storport or minport driver. Here's a MSKB that explains the storage stack.
I don't have a fix for this either but I do wonder if outdated miniport drivers play a role here. Also running ONTAP DSM 4.x (I believe it is 4.0). Using HP rebranded Qlogic cards. Does everyone have Qlogic, I wonder!?