Determining whether shared disks can be used as tiebreaker disks

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You can use the tb_break command to determine whether disks can be used for a shared disk tiebreaker. This command is available with RSCT and can be used with AIX®, Linux® (Power Systems servers, System x platform, and System z® platform), and Solaris. The tb_break command can be used only to determine whether a specific disk can accept an SCSI-2 reservation. It cannot determine whether multiple systems in the domain have access to the disk.

The tb_break command is in the /opt/rsct/bin directory. To use it, you must specify:

An action such as reserve, to lock the disk, or release, to unlock the disk.
The tiebreaker type: DISK, ECKD, or SCSI.
The device. There are different ways to specify the device, depending on the operating system:
- DISK
  This tiebreaker type is for AIX. You can use the device name (/dev/hdisk5) or the PVID of the disk, along with the DEVICE keyword or the PVID keyword as the device.
- ECKD
  This tiebreaker type is for Linux on the System z hardware platform.
- SCSI
  This tiebreaker type is for Linux and Solaris. For the Power Systems servers and the System x hardware platforms, there are two ways to determine the device. You can specify the SCSI bus attributes by using the CHAN, HOST, ID, and LUN keywords, or you can specify a unique identification number. A specification that uses SCSI bus attributes might be similar to the following sample:
```
"HOST=n CHAN=n ID=n LUN=n"
```
  You can specify a unique identification number with the RDAC.WWN keyword or the WWID keyword. Use RDAC.WWN when the SAN disk is being used with the LSI RDAC driver for multipathing. The RDAC.WWN keyword indicates tb_break must verify that the ID is valid. Use WWID if the SAN disk is being used with a pathing driver which supports the SCSI-2 specification. This driver must provide a method for retrieving the unique identifier of the disk. An example is the EMC PowerPath driver, though WWID is not limited to EMC SANs. On Solaris, use the DEVICE keyword to specify the device name that identifies the disk.
- SCSIPR
  This tiebreaker type is for Linux on System x hardware platform and AIX on the Power Systems platform.
  Perform the following steps on all of the remote peer systems to verify whether all the systems support the SCSIPR tiebreaker correctly with the chosen SCSI disk storage device:
  1. Reserve the disk device by using the tb_break command:
```
/opt/rsct/bin/tb_break -v -l -t SCSIPR DeviceInfo_device_specification_for_this_system
```
    This command reserves the disk device.
  2. Try to reserve the same disk device by using the tb_break command on all of the other peer domain systems:
```
/opt/rsct/bin/tb_break -v -l -t SCSIPR DeviceInfo_device_specification_for_this_system
```
    This command fails to reserve the disk device because it is already exclusively reserved by the first system.
  3. Release the disk device by using the tb_break command:
```
/opt/rsct/bin/tb_break -v -u -t SCSIPR DeviceInfo_device_specification_for_this_system
```
    This command releases the disk device.

For example, to issue a reserve command to a disk on Linux, on the Power Systems or System x hardware platforms, run this tb_break command:

tb_break -l -t SCSI "RDAC.WWN=600a0b80000cf57b00000042474304bc"

The following output is displayed:

Initializing SCSI tie-breaker (RDAC.WWN=600a0b80000cf57b00000042474304bc)
WWN (600a0b80000cf57b00000042474304bc) is found at /proc/mpp/C105FastT/virtualLun4
Found: WWN=600a0b80000cf57b00000042474304bc HOST=2 CHAN=0 ID=0 LUN=4
Reserving tie-breaker (RDAC.WWN=600a0b80000cf57b00000042474304bc)
scsi_reserve(/dev/sg4) is granted, status=0
tb_reserve status 0 (errno=0)

To release the reservation, run this tb_break command:

tb_break -u -t SCSI "RDAC.WWN=600a0b80000cf57b00000042474304bc"

The following output is displayed:

Initializing SCSI tie-breaker (RDAC.WWN=600a0b80000cf57b00000042474304bc)
WWN (600a0b80000cf57b00000042474304bc) is found at /proc/mpp/C105FastT/virtualLun4
Found: WWN=600a0b80000cf57b00000042474304bc HOST=2 CHAN=0 ID=0 LUN=4
Releasing tie-breaker (RDAC.WWN=600a0b80000cf57b00000042474304bc)
tb_release status 0 (errno=0)

If the disk is not capable of accepting SCSI-2 reservations, you receive the following error:

tb_break -l -t SCSI "WWID=6005076303ffc4d20000000000001172"
Initializing SCSI tie-breaker (WWID=6005076303ffc4d20000000000001172)
tb_set_error (errid=-1 msg_num=106)error in tb_init(). status=-1

To forcefully break a reservation when the release option fails to release the reservation, use the following command:

/opt/rsct/bin/tb_break -v -b -t <tb_type> DeviceInfo_device_specification_for_this_system