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- From: mark@infocomm.com
- Newsgroups: comp.sys.dec,comp.os.vms
- Subject: Re: Multi-hosting SCSI devices
- Message-ID: <1993Jan22.222010.21719@infocomm.com>
- Date: 22 Jan 93 22:20:10 PST
- References: <1993Jan19.154520.20736@nessie.mcc.ac.uk>
- Organization: INFO COMM - Computer Consulting, Redwood City, Ca
- Lines: 40
-
- In article <1993Jan19.154520.20736@nessie.mcc.ac.uk>, mzagsaa@v4.cgu.mcc.ac.uk (Tony Arnold) writes:
- >
- > I run a LAVC where two of the nodes are a 3600 and a 3400. These nodes each
- > have a CMD CQD223TM SCSI adapter on them and there is a 1Gb disk on each
- > SCSI bus.
- >
- > The CMD controllers support multi-hosting, so it is possible to effectively
- > connect both controllers on the same SCSI bus. The disks would then be
- > accessible from both nodes which would reduce the impact of one or other
- > machines going down.
- >
- > One of the disks is currently the system disk for the cluster. My question,
- > for anyone who may have done this, is it possible to boot both nodes direct
- > from the disk (using separate roots, of course) or do I still have to boot
- > one from the disk and the other remotely via a MOP request?
-
- Both systems can boot directly as long as you can set BFLAGS on one node to
- select an alternate root. The hardware you have may or may not support this.
-
- Now all sounds peachy, but there are several significant caveats:
-
- - SCSI cable length is an issue be sure to keep well within the 5
- meters, and don't try to fill up the SCSI bus with 6 devices.
- - SCSI termination is an issue which implies that even if one node
- goes down you can't simply turn it off without removing power
- on the terminating resistor on one end of the bus. Doing this will
- most likely hang the scsi bus or at least make data corruption VERY
- likely.
- - If you had more powerful CPU's and had more disks on the bus you'd
- also have to worry about controller/qbus bandwidth being a serious
- limitation (especially if you try to do shadowing).
-
- > Tony Arnold,
- > Manchester Computing Centre,
- > OpenVMS Systems Manager.
- --
- --
- Mark Pizzolato - INFO COMM Computer Consulting, Redwood City, Ca
- PHONE: (415)369-9366 UUCP: decwrl!infopiz!mark or uunet!lupine!infopiz!mark
- DOMAIN: mark@infocomm.com
-