I have been under the assumption that SCSI reserve release can cause SAN switches, along with tape libraries, to have to be rebooted. Is this true?

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As long as proper zoning is used in the fabric and LUN security in the storage array, there should be no problem as long as your going through a switch. Using a HUB is a different matter though, since everything on the loop is affected.

SCSI reserve release is used as the locking mechanism for Microsoft clustering in MSCS to handle ownership of the Quorum resource. Most SAN implementations support MSCS with no issues at all. Switches are point to point, so the SCSI traffic between an initiator and target should not affect the nodes or devices attached to the other ports of the switch. This is why SAN based backup solutions work so well. Tapes are on one port and disks on the others. Tape drive rewind commands tend to use a SCSI reset on the path, which is not very good for disk traffic! This is why you should never put disk and tape on the same loop in an FC-AL Hub based SAN. The same holds true for shared public loop connected devices to the same side of a Brocade QuickLoop port.

Chris

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This was first published in March 2002

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