News Column

Patent Issued for SCSI Reservation Status Information on a SAN Disk

February 13, 2014

By a News Reporter-Staff News Editor at Computer Weekly News -- International Business Machines Corporation (Armonk, NY) has been issued patent number 8639856, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Anumalasetty, Kiran K (Bangalore, IN); Ham, Nicholas S (Austin, TX); Jasti, Purna Chandra (Madhapur, IN); Maddali, Sudhir (Hyderabad, IN); Rajaboina, Yadagiri (Madhapur, IN); Rathi, Sanket (Hyderabad, IN).

This patent was filed on August 4, 2011 and was published online on January 28, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention relates generally to a data processing system and computer program product for obtaining Small Computer System Interface (SCSI) reservation status information on a storage area network (SAN) device. More specifically, the present invention relates to determining if a SAN device is reserved, under which standard or protocol it is reserved under, as well as other details concerning reservations.

"Data centers are routinely being expanded and/or maintained to add or replace processors, each of which may be a part of a host. In order to enhance utilization, each host may be assigned or otherwise reserve use of storage. Hosts may use one of the SCSI protocols to reserve a disk, using a standard in accordance with SCSI primary commands (SPC), as promulgated by T10 technical committee of the International Committee for Information Technology Standards (INCITS).

"Currently, there are two standards in use to reserve storage in the form of logical units. A logical unit or logical unit number (LUN) is one or more disk drives or other SCSI capable devices that are addressable as a unit and is presented to a host via one or more storage controllers. The protocols for communicating from a host, also known as a SCSI Initiator, to a LUN, also known as a SCSI target, can be, for example SPC-2 or SPC-3. The SPC specifies various SCSI commands according to various versions of protocols. SPC-Version 2, equivalently referred to as SPC-2, is a version of commands published in 2001. SPC-Version 3, equivalently referred to as SPC-3, is a version of commands published in 2005. In the case of SPC-2, the reservation mechanism uses RESERVE and RELEASE SCSI commands. In the case of SPC-3, the reservation mechanism uses persistent reservation (PR) SCSI Commands.

"LUNs, as shipped, may have the SCSI protocol state machine installed in the form of firmware. Hosts communicating with the LUN have the flexibility to use either of the SCSI Reservation mechanisms (SPC-2 Reserve/Release or SPC-3 Persistent Reservation commands). However, hosts cannot use both the Reservation mechanisms at the same time even though the LUN supports both the Reservation mechanisms. This situation poses a challenge for the host in terms of communicating with the LUN to obtain its current reservation status.

"Accordingly, a remedy is sought."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "A computer implemented method for determining reservation status information for a logical unit number (LUN). A host transmits a persistent reservation in command with read reservation to a first LUN, wherein the host is connected to a port of the data storage server to which the first LUN belongs. The host receives a message from the first LUN. The host determines that the message is a success message. The host, responsive to a determination that the message is a success message, sends to the first LUN, a persistent reservation with read keys. The host determines that the first LUN responds with a zero data length. The host, responsive to a determination that the first LUN responds with a zero data length, sends a SCSI command test unit ready to the first LUN. The host determines that the test unit ready (TUR) succeeds. The host, responsive to a determination that the TUR succeeds, verifies a reservation policy attribute of the first LUN."

For the URL and additional information on this patent, see: Anumalasetty, Kiran K; Ham, Nicholas S; Jasti, Purna Chandra; Maddali, Sudhir; Rajaboina, Yadagiri; Rathi, Sanket. SCSI Reservation Status Information on a SAN Disk. U.S. Patent Number 8639856, filed August 4, 2011, and published online on January 28, 2014. Patent URL:

Keywords for this news article include: International Business Machines Corporation.

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Source: Computer Weekly News

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