Unit attention and SAM

Tom Wicklund wicklund at intellistor.com
Wed Jul 13 15:31:28 PDT 1994

The SCSI Architecture Model describes Unit Attention conditions
(section 4.6.5) as being kept on a per initiator, per logical unit
basis, as SCSI-2 defines Unit Attentions.

How is this reconciled with the advent of 64 bit initiator
identifiers?  It appears that a protocol which uses an N bit address
(e.g. FCP appears to use a 24 bit address) requires that the target
keep 2**N bits for each Unit Attention condition possible.  For power
on reset alone, this implies that an FCP device must have 2MB of
memory just to keep power on reset bits in order to comply with SCSI.

Is there some sort of limitation on the number of initiators a device
can talk to between power cycles or other method to limit this?  Or
are SCSI-3 devices required to keep per-initiator unit attention
status for all possible devices?

Thomas Wicklund
Fujitsu Computer Products of America

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