Logical Unit Number(LUN) 0, a SCSI Requirement
Last updated on MAY 10, 2017
Applies to:Solaris Operating System - Version 8.0 and later
This article is intended to explain the importance of having a Logical Unit Number(LUN) 0 on any storage array.
A few issues in the field have been reported, where, depending on the array, problems have been seen on hosts connected to arrays without a LUN 0. While this Technical Instruction shows examples of Sun StorEdge[TM] 3510 and SE6x20 arrays specifically, it can apply to other storage. However, that still needs to be verified.
LUN 0, is a Small Computer Systems Interface(SCSI) protocol requirement, and needs to exist for proper communication with the driver.
In SCSI-3, this requirement is explicitly stated in the SCSI standards documentation - SAM-2 section 4.7.2 SCSI target device.
In SCSI-2, the requirement is implicit in the first sentence of X3T9.2375D (SCSI-2 section 22.214.171.124)
Also, from Sun's very first Hardware RAID array, the RSM2000 / Sun StorEdge[TM] A3000 and onward, the array management software has always depended on LUN 0 being available. Not having a LUN 0 was unqualified and has typically always led to unexpected behavior.
As an example, with the Sun StorEdge [TM] 351x and SE99xx families of arrays that are able to present multiple (SCSI-) targets on a single host-channel, it is even more important to realize that every attached host MUST be able to communicate with a LUN 0 on EVERY presented target in order to ensure proper operation.
In some cases this requirement even leads to having to map multiple different LUN 0's on the same (SCSI-) target, most commonly when LUN security (World Wide Number(WWN)) filtering is being used.
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