Method and apparatus for identifying multiple paths to a SCSI device

• US 20040064594A1
• Filed: 10/01/2002
• Published: 04/01/2004
• Est. Priority Date: 10/01/2002
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Krishnamurthy, Vikram, Pooni, Subramaniyam, Mangalore, Rajkumar, Srinath, Vijay
• Granted Patent: US 7,069,354 B2
• Time in Patent Office: Days
• US Class Current: 710/1
• CPC Class Codes: G06F 13/423 with synchronous protocol

Abstract

The method includes querying for one or more logical unit numbers (LUNs) pertaining to a small computer system interface device, each LUN representing a potential path from a host to the SCSI device. Response data indicative of multiple devices, with each separate instance representing a different SCSI separate instances of independent SCSI devices, with each separate instance representing a different SCSI device structure. A unique identifier (UID) is calculated for each SCSI device structure, from which a device file is generated based on the UID and contains UID and path information that differentiates between multiple paths from the host to the SCSI device.

Claims

1. A method for identifying multiple paths from a host to a small computer system interface (SCSI) device, comprising the steps of:

querying for one or more logical unit numbers (LUNs) pertaining to the SCSI device, each LUN representing a potential path from the host to the SCSI device;

treating response data indicative of multiple LUNs to the SCSI device as separate instances of independent SCSI devices, each separate instance representing a different SCSI device structure;

calculating a unique identifier (UID) for each SCSI device structure; and

generating a device file based on the UID, the device file containing UID and path information that differentiates between multiple paths from the host to the SCSI device.

2. The method of claim 1, wherein the path information includes a <

host, bus, target, LUN>

address of a particular path to the SCSI device.

3. The method of claim 1, wherein the querying step includes issuing one or more SCSI commands.

4. The method of claim 1, further comprising:

mapping the calculated UID to the SCSI device structure.

5. The method of claim 4, further comprising:

adding the SCSI device structure to a list of other SCSI device structures that map to the same UID.

6. The method of claim 1, further comprising:

storing the device file by its device file name in one of a plurality of directories containing device file names for different types of SCSI devices.

7. The method of claim 1, wherein the host can distinguish between each multiple path to the same SCSI device by the device file name, thereby providing a fault tolerance capability for the host.

19. A method by which a user mode application obtains all physical paths that point to a logical unit on a small computer system interface (SCSI) device, comprising:

sending an input output control (IOCTL) to a kernel component; and

receiving all <

host, bus, target, LUN>

-encoded addresses that map to a known unique identifier (UID) for the logical unit from the kernel component, the UID being available from a device file generated in accordance with claim 1.

8. An apparatus for identifying multiple paths from a host from a host to a small computer system interface (SCSI) device, comprising:

means for querying the SCSI device to determine if there are one or more logical unit numbers (LUNs) pertaining to the SCSI device, each LUN representing a potential path from the host to the SCSI device;

means for treating responses containing data indicative of multiple LUNs as separate instances of independent SCSI devices, each separate instance representing a different SCSI device structure that pertains to the SCSI device;

means for calculating a unique identifier (UID) for each SCSI device structure; and

means for generating a device file based on the UID, the device file containing UID and path information that differentiates between multiple paths to the same SCSI device.

9. The apparatus of claim 8, wherein the path information is path information having a <

host, bus, target, LUN>

encoded-address of a particular path from the host to the SCSI device.

10. The apparatus of claim 9, further comprising

means for mapping the calculated UID to the SCSI device structure.

11. The apparatus of claim 10, further comprising

means for adding the SCSI device structure to a list of other SCSI device structures that map to the same UID.

12. The apparatus of claim 9, further comprising means for storing the device file by a device file name in memory.

13. The apparatus of claim 12, wherein the means for storing further includes a plurality of directories containing device file names for different SCSI devices.

14. The apparatus of claim 13, wherein one of the directories stores generated device files for disk drivers, the device file name being in a format <

COMPRESSED_UID>

-<

PATH_NO>

-<

PARTITION_NO>

, where COMPRESSED_UID represents a UID-based SCSI device name, PATH_NO differentiates between multiple paths to the single SCSI device, and PARTITION_NO is a specific partition on the disk.

15. The apparatus of claim 13, wherein one of the directories stores generated device files for tape drivers, the device file name being in a format [n]<

COMPRESSED_UID>

-<

PATH_NO>

-<

SCSI DEVICE_CHARACTERISTICS>

, where COMPRESSED_UID represents a UID-based SCSI device name, PATH_NO differentiates between multiple paths to the single SCSI device, and SCSI DEVICE_CHARACTERISTICS pertains to characteristics of a tape LUN.

16. The apparatus of claim 13, wherein one of the directories stores generated device files for generic drivers, the device file name being in a format <

COMPRESSED_UID>

-<

PATH_NO>

, where COMPRESSED_UID represents a UID-based SCSI device name, and PATH_NO differentiates between multiple paths to the single SCSI device.

17. The apparatus of claim 8, wherein the SCSI device is a logical unit contained within a SCSI device that is connected to one or more of a SCSI bus and a fibre channel bus.

18. The apparatus of claim 8, wherein the host can distinguish between each multiple paths to the same SCSI device by the device file name, thereby providing a fault tolerance capability for the host.