Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!agate!dog.ee.lbl.gov!elf.ee.lbl.gov!torek From: torek@elf.ee.lbl.gov (Chris Torek) Newsgroups: comp.unix.admin Subject: Re: Fujitsu 1.2Gb disk on Sun Message-ID: <13093@dog.ee.lbl.gov> Date: 11 May 91 14:23:37 GMT References: <1991May9.191941.2377@mprgate.mpr.ca> Reply-To: torek@elf.ee.lbl.gov (Chris Torek) Organization: Lawrence Berkeley Laboratory, Berkeley Lines: 18 X-Local-Date: Sat, 11 May 91 07:23:37 PDT The `magic limit' for old SCSI is 2 097 152 blocks. These drives have 512-byte blocks, so that is 1 073 741 824 bytes. This limit occurs because the 6-byte SCSI read and write commands store the block number in 21 bits. The solution is to use the 10-byte SCSI read and write commands, which have a 32 bit field and can address 4 294 967 296 blocks or, with 512 byte blocks) 2 199 023 255 552 (2 terabytes). With 1024 byte blocks the addressibility doubles; the 10-byte command are unlikely to be a problem for some time. How many SCSI disk controllers (targets) do *not* support 10-byte commands? My driver assumes all disks do, for now, but it would be easy to choose 6-or-10 based on the capacity returned or, if necessary, each block number. -- In-Real-Life: Chris Torek, Lawrence Berkeley Lab CSE/EE (+1 415 486 5427) Berkeley, CA Domain: torek@ee.lbl.gov