Question about SCSI support for active/passive disk arrays

Patrick Stirling pms at
Tue Aug 29 10:37:38 PDT 2000

* From the T10 Reflector (t10 at, posted by:
* Patrick Stirling <pms at>
Hi all,

I'm working on the "Storage Appliance" project at Veritas. This is
essentially a smart disk array, not altogether unlike EMC's Symmetrix or
Sun's "purple". It will provide "active/passive failover" - that is, a
given "virtual disk" will be accessible via LUNs on more than one port
(Host Bus Adapter), but will be active on only one - i.e. the data can be
accessed on only one port at a time. If a component of the path to this
port fails, multi-pathing software on the machine using the storage can
send a Vendor Unique SCSI command to a "passive" LUN for this disk to
cause a failover so that the data can be accessed through the other LUN.

Now, my question is, has there been any discussion on this forum of
this? Several vendors have this type of setup so it seems reasonable to
define a standard SCSI command to request failover.

At the moment I'm planning to use two 6-byte (group1) SCSI commands to
request failover and to check whether the addressed LUN is active (call
them "SET ACTIVE" and "GET ACTIVE"). It's been suggested that a 10-byte
command is more appropriate as that name-space is larger (less likelihood
of clashing). A mode select page is another possibility, although I prefer
a CDB.

Another aspect is the Sense codes for these commands.

Any comments would be welcome!

Patrick Stirling
VERITAS Software Corp.

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