stockett@earth.tsd.arlut.utexas.edu (Jeffrey Stockett) (04/16/91)
Has anyone out there ever seen a case where more than one SCSI initiator (typically a computer's host adapter) is communication with a single SCSI target (typically a mass storage device)? There is brief reference to this in the American National Standard's SCSI reference, but I have yet to see it in reality. The scenario would go like this: two or more computers talking two one SCSI device via the SCSI bus. Sounds crazy, but it would be very useful in some cases. If anyone out there has either accomplished this, or has seen or heard of it, please let me know. Thanks in advance, Jeffrey M. Stockett Applied Research Laboratories Internet: stockett@titan.tsd.arlut.utexas.edu UUCP: ..cs.utexas.edu!ut-emx!jeanluc!jeffms
feustel@netcom.COM (David Feustel) (04/16/91)
I tried this with two adaptec 1542A controllers and one Conner SCSI drive. Didn't work. Found out within the last week that the 1542a "wasn't designed with this scenario in mind." Too bad. I've gone back to IDE drives and am now waiting for FDDI. -- David Feustel, 1930 Curdes Ave, Fort Wayne, IN 46805, (219) 482-9631 EMAIL: netcom.com
duckie@cbnewsj.att.com (john.c.mc millan) (04/16/91)
Sane or not, we run a cluster of 3 AT&T 3B2/700's which "share" SCSI buses.
Each UNIX system has:
- one Single-Ended, internal SCSI bus with its core UNIX facilities:
+ 2 or 3 disks [incl. file systems ROOT, /usr, SWAP...]
+ 1 Exabyte tape
+ "other tapes" -- 9 track, cartridges, etc.
- two Differential SCSI buses shared across all three 3B2's:
+ DS0= 3 Host Adapters + 3 dual-disk targets
+ DS1= 3 Host Adapters + 2 dual-disk targets + 2 single-disks
We found the cluster was more reliable with the Exabytes un-shared.
The other tapes only had S-E adapters.
Re-booting can be a bit dicey: the reboot diagnostics of the 3B2
occasionally confuse the running systems regarding a shared bus.
Occasionally, we have simultaneously mounted a partition read-only
on several systems. Typically, however, we use RFS for file system
sharing and the 3B2's may share drives but not partitions of those
drives.
If a 3B2 crashes, the other two systems can FSCK the damaged
file systems while the crashed 3B2 is receiving special attention.
When a system is taken out of service for an extended interval,
the file systems it usually directly mounts -- and makes available
to other systems via RFS -- are mounted by the other two 3B2's
and made available via RFS. Since the disks are already cabled
in to each system, this transfer is done without taking down
the systems.
Nuff' said. I presume this is the manner of target sharing to which
you were refering.
John McMillan -- jcm@pegasus.att.com -- muttering for self, onlywicklund@intellistor.com (Tom Wicklund) (04/17/91)
Multiple initiators on a SCSI bus should work without any problems. However, this is not a common implementation compared to the more traditional single initiator environment. A well designed SCSI product which implements the features necessary for multiple initiator (e.g. BUSY status from the device) shouldn't have any problems. A product designed for a single initiator mass market (e.g. most PC host adapters) may not have multiple initiator support built in. A product designed to implement the full SCSI standard will. I am aware of one product which will handle multiple initiators on a PC bus -- Ciprico's Rimfire 5500 PC/AT host adapter (I used to work at Ciprico and can attest to many hours of 2 or more PCs pounding on one drive). I imagine some other high end products (such as from DPT) will also work.
kev@hpcpbla.HP.COM (Kevin Jones) (04/17/91)
1. Single Initiator - Single Target 2. Single Initiator - Multiple Targets 3. Multi Initiator - Single Target 4. Multi Initiator - Multiple Targets Most SCSI implementations have reached "2" of the above. The SCSI spec allows for all of the above. Whether or not you can do "3" or "4" depends on how well "SCSI" has been implemented on the particular hosts and targets you have in mind. A number of SCSI implementations can't handle "more than one thing at once". This is either because their designers didn't design the functionality in, or they couldn't be bothered to test/fix/get-the-thing-working. The answer to your question is therefore: "It Depends.....". My guess is that if the Target is a disk drive then you should be able to get a disk that can work with multiple hosts. If your target is a tape/printer/plotter/scanner then you might have to hunt for one that supports this featurism since multi-host support ain't much of a issue for these types of peripherals. Regards, Kevin Jones. ----------------------------------------------------------------- Kevin Jones. | Hewlett Packard Ltd, | Computer Peripherals Bristol, kev%hpcpbla@hplb.hpl.hp.com | Filton Road, | Stoke Gifford, Tel: 011 44 272 799910 (ext 22351) | Bristol. BS12 6QZ. | ENGLAND. ----------------------------------------------------------------- This response does not represent the official position of, or statement by, the Hewlett-Packard Company. The above data is provided for informational purposes only. It is supplied without warranty of any kind.