Path: utzoo!telly!attcan!seachg!burke From: burke@seachg.uucp (Michael Burke) Newsgroups: comp.periphs.scsi Subject: Re: Two HAs on single SCSI bus Message-ID: <1991Mar27.175719.3474@seachg.uucp> Date: 27 Mar 91 17:57:19 GMT References: <55@opel.COM> Reply-To: burke@seachg.UUCP (Michael Burke) Organization: Sea Change Corporation, Mississauga, Ontario, Canada Lines: 46 In article <55@opel.COM> johnk@opel.COM (John Kennedy) writes: >Are there any SCSI implementations available that allows use of two >host adapters on a single bus? Specifically, I want to dual-port >a disk drive by such a configuration as this: > > > ____________ ____________ >| | | | >| | | | >| CPU A | SCSI bus | CPU B | >| |================================| | >|____________| || |____________| > ____ > (____) > |disk| > |____| > >Is this what differential SCSI is? Is there any good published material on >the subject? > >The goal is to have two redundant CPUs able to access the same data (not >necessarily at the same time, but that would be great). > >-- >John Kennedy johnk@opel.COM >Second Source, Inc. >Annapolis, MD Yes, one can configure a SCSI channel as above. A problem may occur if the two hosts try to access the data at the same time (in Unix each host "owns" the super block). Even in this situation you can get around the problem by having two partitions, each host "owning" one partition. We have at least one customer who has a similar configuration, ie two hosts with one disk drive and several SCSI tape drives shared. Both SE and DIFF SCSI support this type of connection. -- --- Michael Burke Sea Change Corporation 6695 Millcreek Drive, Unit 8 Mississauga, Ontario, Canada L5N 5R8 Tel: 416-542-9484 Fax: 416-542-9479 UUCP: ...!uunet!attcan!seachg!burke