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Task Management Propagation in a Device Containing Multiple Access Ports

IP.com Disclosure Number: IPCOM000013578D
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Abstract

In a Storage Area Network a storage device may have more than one access path to an individual server. The storage device may also have more than one access path to a group of servers running a common application across the group of servers. If the storage device presents multiple access ports for the servers to connect to then the servers will need to coordinate their activities to ensure proper operation across multiple ports.

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Task Management Propagation in a Device Containing Multiple Access Ports

  In a Storage Area Network a storage device may have more than one access path to an individual server. The storage device may also have more than one access path to a group of servers running a common application across the group of servers. If the storage device presents multiple access ports for the servers to connect to then the servers will need to coordinate their activities to ensure proper operation across multiple ports.

  For instance in Figure 1, server 101 using the SCSI RESERVE command reserves Virtual Device 501 via port 401-1 of storage array controller 401 in storage array 201 through host bus adapter (HBA) 101-1. The only standard mechanism to clear the reservation is provided to the server HBAs also attached to port 401-1. In order for server HBA connected to port 402-1 to obtain a device reservation through port 401-1 some mechanism must be provided to the server application to clear the device reservation via port 401-1 prior to establishing the reservation via port 402-1.

  The controllers 401 and 402 in storage array 201 may provide a mechanism to propagate SCSI task management functionality internally so that an internally generated task management function is passed through to the appropriate port controllers 401 and
402.

  Here is an example also using Figure 1. Server 101 issues a SCSI RESERVE command to reserve Virtual Device 501 via HBA 101-1 attached to port 401-1 of controller
401. At a later time the cable connected to port 401-1 is disconnected. Server 101 discovers that the path to device 501 is lost and switches to its alternate path through HBA 101-2 and port 402-1 of controller 402. Under normal circumstances, to clear a reservation the host must issue a SCSI R...