ccocsnp@prism.gatech.EDU (Nick Pope (IBM Technical Support)) (03/16/91)
I just saw a question about drives larger that 1.2GB under VMS.... I quote from "Digital NEWS, March 4, 1991 front page." : " Customers configuring Ultrix and some VMS systems with SCSI ... hard disk drives of more than 1 GByte run a serious risk of losing their stored data. The SCSI implemention found in Ultrix and all VMS operating systems except version 5.4 is unable to address hard disk drives larger than 1 GByte, meaning that users with disks formatted at more than 1 GByte are paying for storage space they cannot possibly access. And, in attempting to do so, they could lose all their data. The problem, which is being reported by users, systems integrators and vendors of the increasingly popular large-capacity drives, does not occur when using a later version of the SCSI I/O driver called extended SCSI. According to SCSI specialists, the SCSI Group 0 set of commands, which are also embedded into some of Sun Microsystems Inc. and virtually all Apple Computer Inc. operating systems can address a maximum of 1.073742 GBytes. On disks of a larger capacity , the SCSI I/O driver wraps around the disk and overwrites the first block of data, called the superblock or home block..." it goes on to explain that group 0 commands only allocate 6 bytes to address disk bytes (thus the 1 Gig limit). Also the problem is found in all current versions of Ultrix up to 4.1. So in order to safely hook up a >1.0 gig HD you need VMS 5.4 or >Ultrix 4.1. hope this helps.... Nick Pope (cc100np@prism.gatech.edu or ccocsnp@prism.gatech.edu)