saaf@joker.optics.rochester.edu (Lennart Saaf) (10/05/89)
Is it possible to run two Macs off one hard disc? I assume that each Mac must boot off its own copy of System (and Finder?). Could this be done using the Blesser application? Or can the disc be partitioned to look like two separate discs? If it is possible, is it also incredibly slow? Thanks, Len -- ------------------------------------------------------------------------ | Len Saaf, The Institute of Optics, Univ. of Rochester, Rochester, NY | | Internet: saaf@joker.optics.rochester.edu Bitnet: SAAF@UOROPT | ------------------------------------------------------------------------
gford@nunki.usc.edu (Greg Ford) (10/05/89)
In article <SAAF.89Oct4151933@joker.optics.rochester.edu> saaf@joker.optics.rochester.edu (Lennart Saaf) writes: >Is it possible to run two Macs off one hard disc? I assume that each >Mac must boot off its own copy of System (and Finder?). Could this be >done using the Blesser application? Or can the disc be partitioned to >look like two separate discs? If it is possible, is it also >incredibly slow? > >Thanks, >Len > >-- >------------------------------------------------------------------------ >| Len Saaf, The Institute of Optics, Univ. of Rochester, Rochester, NY | >| Internet: saaf@joker.optics.rochester.edu Bitnet: SAAF@UOROPT | >------------------------------------------------------------------------ Well, Len, I didn't think it would work, but I did hook up two macs to one (two actually, read on) drive(s). I personally didn't think it would work, but I tried it anyway. All I did was run a scsi cable from my Mac II to a friend's SE. He turned his computer on (the SE) and it booted off my HD (a Rodime 140 Meg, scsi 4). Naturally, I was surprised. Anyway, he was doing his thing with my HD and I was doing my thing with my HD, and didn't have any trouble at all. It did, however, *seem* to give me preference on the HD though. Wonders never cease.... I retried the little "experiment" with an SE that had it's own HD. Of course, it was set to a different scsi # (6 I think). Anyway, not only could he mount my disks on his desktop, I could mount his disks on mine. (I say disks, because both of us had true partitions). Kinda neat. -- ******************************************************************************* * Greg Ford GEnie: G.FORD3 * * University of Southern California Internet: gford%nunki.usc.edu@usc.edu * *******************************************************************************
cramer@sun.com (Sam Cramer) (10/06/89)
Don't Macs reserve SCSI ID 7 for themselves? If so, it seems like having two SCSI devices on the bus with the same ID is a bad idea. On the other hand, maybe it all works out because Macs do polled I/O, so one Mac grabs the bus until the SCSI command is completed. Sam
kevind@pogo.WV.TEK.COM (Kevin Draz) (10/06/89)
In article <SAAF.89Oct4151933@joker.optics.rochester.edu> saaf@joker.optics.rochester.edu (Lennart Saaf) writes: >Is it possible to run two Macs off one hard disc? I assume that each >Mac must boot off its own copy of System (and Finder?). Could this be >done using the Blesser application? Or can the disc be partitioned to >look like two separate discs? If it is possible, is it also >incredibly slow? > No. The SCSI bus can only have one controller, device #7, and the Macintosh is very "hard wired" to be device #7. It is, however, possible to use something like TOPS to have a non-dedicated file server, and a floppy-only client machine, although at least an SC20 type drive would make life easier on the client. -- ---- kevind@pogo.wv.tek.com Tektronix Color Printers Technical Support
sklein@cdp.UUCP (10/06/89)
People have run two Macs from one hard disc, but Jim Reekes at apple says you're asking for MAJOR PROBLEMS because of the SCSI conflict (both Macs will have the SCSI ID=0). So, DON'T DO IT! -shabtai (e-mail addresses/long sig follow) UUCP: uunet!pyramid!cdp!sklein | BitNet: cdp!sklein%labrea@stanford Internet: cdp!sklein@arisia.xerox.com | Phone: (301) 270-2250 "You can't always get what you wan't" -- Rolling Stones "You can get it if you really want" -- Jimmy Cliff
kaufman@Neon.Stanford.EDU (Marc T. Kaufman) (10/06/89)
In article <125867@sun.Eng.Sun.COM> cramer@sun.com (Sam Cramer) writes: >Don't Macs reserve SCSI ID 7 for themselves? If so, it seems like having >two SCSI devices on the bus with the same ID is a bad idea. On the other >hand, maybe it all works out because Macs do polled I/O, so one Mac grabs >the bus until the SCSI command is completed. Polling would work if the SCSIGet/SCSISelect routines would perform a Bus Arbitration phase before blasting stuff out on the Bus. Unfortunately, under the current OS (6.x), they do not. Also, I would be VERY careful if a volume was simultaneously mounted on two systems. The Volume Control Blocks and allocation maps are almost certainly guaranteed to get out of Sync, since there is no way for one Mac to tell the other that they have been changed. One possible problem, EVEN WITH ARBITRATION, is that if both Macs tried to select simultaneously, they could not tell who won because they both would be setting the same selection bit (bit 7). In general, then, this is NOT a good idea. Keep your copy of the SUM utilities handy. Marc Kaufman (kaufman@Neon.stanford.edu)
ts@cup.portal.com (Tim W Smith) (10/07/89)
You can probably make it work, although I wouldn't do it with MY data. The first problem is that the Mac uses ID 7. This could probably be gotten around with a patch to the SCSI Manager. However, there is a more serious problem. Does Apple do arbitration? A single initiator SCSI system is allowed by the ANSI standard to skip the arbitration phase. It can just go right into selection. If Apple does this ( and I think they do, at least on the plus ), you could have serious problems if both Macs try to access the bus at the same time. If you are willing to rewrite the SCSI Manager, of course, you can get around these problems. Tim Smith
wasilko@netcom.UUCP (Jeff Wasilko) (10/07/89)
In article <141200079@cdp> sklein@cdp.UUCP writes: > >People have run two Macs from one hard disc, but Jim Reekes at apple >says you're asking for MAJOR PROBLEMS because of the SCSI conflict >(both Macs will have the SCSI ID=0). So, DON'T DO IT! ^^^^^^^^ Macintoshes are set up with th SCSI ID=7, not 0. >-shabtai >(e-mail addresses/long sig follow) >UUCP: uunet!pyramid!cdp!sklein | BitNet: cdp!sklein%labrea@stanford >Internet: cdp!sklein@arisia.xerox.com | Phone: (301) 270-2250 >"You can't always get what you wan't" -- Rolling Stones >"You can get it if you really want" -- Jimmy Cliff -- Jeff Wasilko wasilko@netcom.uucp uunet!apple!netcom!wasilko netcom!wasilko@apple.com
earleh@eleazar.dartmouth.edu (Earle R. Horton) (10/08/89)
Worse than any possible electronic incompatibility is the fact that the Macintosh File Manager has no means to synchronize disk operations between two Macs on one file system. Mount one HD on two Macs, do anything significant with files on the disk, and you will sooner or later get data corruption. If this data corruption involves the disk directory, then all files on the disk might be lost. Earle R. Horton
Adam.Frix@f200.n226.z1.FIDONET.ORG (Adam Frix) (10/08/89)
sklein writes: > People have run two Macs from one hard disc, but Jim Reekes > at apple says you're asking for MAJOR PROBLEMS because of > the SCSI conflict (both Macs will have the SCSI ID=0). So, > DON'T DO IT! -shabtai You mean, someone at APPLE COMPUTER told you that "both Macs will have the SCSI ID=0"??????????????? You ARE talking about that computer company in CUPERTINO, CALIFORNIA, right? last I heard Macs have SCSI IDs of 7. Hardwired, non-changeable. --Adam-- -- Adam Frix via cmhGate - Net 226 fido<=>uucp gateway Col, OH UUCP: ...!osu-cis!n8emr!cmhgate!200!Adam.Frix INET: Adam.Frix@f200.n226.z1.FIDONET.ORG
time@oxtrap.oxtrap.UUCP (Tim Endres) (10/12/89)
In article <7961@pogo.WV.TEK.COM> kevind@pogo.WV.TEK.COM (Kevin Draz) writes:
No. The SCSI bus can only have one controller, device #7, and the Macintosh
is very "hard wired" to be device #7.
This misconception still prevails! :)
SCSI has *initiators* and *targets*.
*ANY* Device on the SCSI bus can be an initiator.
*ANY* Device on the SCSI bus can be a target.
*ANY* Device on the SCSI bus can be both.
It just so happens that the Mac is *programmed* to be an initiator.
It would be cool for the Mac to be a target that looked like its own
hard disk! It would also be cool if its SCSI ID were configurable.