On Thu, 17 Jan 2013 22:26:58 -0500, Shmuel Metz (Seymour J.) <[email protected]> wrote:
>The original code base precedes FBA. Once they added FBA most of the >work was done for FCP SCSI. I'm not sure what you're saying. MVS, VM, and VSE code bases *all* precede the invention of channel-attached FBA. They weren't engineered for use by MVS (e.g. originally no RESERVE/RELEASE), but it didn't matter since MVS wasn't engineered to accept device geometries that weren't based on (CYL, TRK, REC) addressing and allocation units. The CMS and CP file systems are based on fixed-size blocks, hiding the device geometry. Further, all usage by CP and CMS is on cylinder boundaries. So from both an application and dasd management perspective, FBA didn't present a huge problem for the people and programs involved. But adding SCSI device drivers was a Big Deal, requiring a lot of heavy lifting, and introducing a lot of new configuration and terminology (WWPN, LUN, NPIV) into the host OS. In VM, you either give the guest direct access to an HBA and let the guest talk to the device, or you use EDEVICEs, wherein CP will emulate FBA minidisks on SCSI LUNs. More interesting, I think, are the cultural barriers to SCSI, particularly with z/OS. When you use SCSI, you (the sysprog) typically don't own or manage the storage. It isn't typically directly plugged into your z box, but is part of a storage area network (SAN) with its own connectivity, performance, security, and recovery technologies (e.g. no IOP-managed multipathing) and management endpoints. You are beholden to and dependent on other admins in other lines of management. I have to say that this doesn't sit will with many mainframe shops that have been bastions of glass-house self-sufficiency for generations. And the consultants have to scramble, too, since all the rules of thumb change. Folks like to look for cheaper dasd, and I don't blame them, but I have to say 'be careful what you wish for.' :-) Alan Altmark IBM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
