X3T10/94-233, Revision 1: Improvements for multi-port environments

Gene Milligan Gene_Milligan at notes.seagate.com
Mon Nov 28 09:40:15 PST 1994

Charles wrote: Note also, that the issue of multiple ports is irrelevant. What
you've defined
>is a set of desirable features that can be applied to any multi-initiator
>environment, irrespective of the number of ports.
 Maybe but, consider two fault resilient scenarios:
Common to each scenario is that I have paid for a disc drive which beyond a lot
of capacity, the yucky word "blazing" performance, and SCSI has two connectors
which at the buyer's option can be connected to one or two SCSI busses. When
connected to one bus it can be connected once with one SCSI ID or twice with
two SCSI ID's. The rest of the characteristics are left to the reader of SCSI
standards, drive specifications, IDENTIFY, INQUIRY, and MODE SENSE pages to
Scenario 1) I have plenty of money and worry a lot so I buy two host bus
adapters, lots of special software, and connect the drive up to both HBAs in
case a cable goes bad (since I walk on them a lot while I worry). Some software
will only talk to the drive through one path. An operator command is required
to switch the path with that software in the case of a failure. Other software
accesses the drive over either path depending upon bus contention.
Scenario 2) I don't have that much money so I buy just one HBA since this is
the normal configuration and all the software I already have understands that.
But I buy one additional turbo software package that will fire up a bigger
"blaze" and connect both of my connectors (ports) to the one bus assigning the
drive two IDs. The software that is incompatible with my turbo charger has to
have an operator configuration command to change the ID by which it accesses
the drive. The turbo charger compatible software accesses the drive with both
IDs using the algorithm for ID selection widely discussed in various Internet
Scenario 3) Having a passing knowledge of the state of the software art there
is no way that I will trust my data to be handled with two different IDs
simultaneously and I need to watch my spending. So I buy one HBA and two
cables. The second cable I keep hermetically sealed in a fruit jar in the
closet with the lights turned off. Only in the event of a failure will I
disconnect the troublesome connection and apply my saved cable to the other
connector on the drive hopping that the connector on the HBA is not the
problem. (These are scenarios not bad feelings about connectors.)
 OK. For the three scenarios how many world wide unique identifications should
the single disc drive have and how should it know when to apply them(it)?
Gene Milligan -- Gene_Milligan at notes.seagate.com
Seagate Technology   -   920 Disc Drive   -   Scotts Valley, CA 95066 USA
Main Phone 408-438-6550   -   Email Problems postmaster at notes.seagate.com
Technical Support: BBS 408-438-8771  Fax 408-438-8137  Voice 408-438-8222  

### OGATE Version 8 message trace and attachment information:
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### Org Date:    11-28-94 07:50:41 AM
### From:        Gene Milligan at SEAGATE
### To:          scsi @ wichitaks.ncr.com @ internet
### Subject:     RE: X3T10/94-233, Revision 1: Improvements for multi-port environments
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