Removing persistent reserves for Tru64 UNIX 5.x

This section explains how to remove persistent reserves for the Tru64 UNIX^® 5.x host system.

In the clustered environment, Tru64 5.x hosts place a persistent reserve whenever you assign a LUN. If you perform a FlashCopy^® or Remote Mirror and Copy operation on a LUN that has persistent reserve, it will fail. If you want to perform a FlashCopy or Remote Mirror and Copy operation, remove the persistent reserve on the target LUN before you assign the LUN.

For example, assume that there are two Tru64 5.x hosts, Alpha1 and Alpha2. The connections available for accessing storage unit LUNs with fibre:

Fibre connection: One fibre connection goes from the KGPSA-xx card in Alpha1 to a switch. One fibre connection goes from the Alpha2 to the switch and another fibre connection goes from the switch to the storage unit.

Use a storage unit volume, for example 10a-21380, as a target LUN to perform a FlashCopy. There are two hosts and four connections: two from Alpha1 and two from Alpha2. The storage unit volume 10a-21380 has four registrants. One registrant is reserved. Use the essvol script to find the devices that are associated with storage unit volume 10a-21380 on each Trucluster node. Figure 1 shows an example of how to remove a persistent reserve when you use the essvol script.

Figure 1. Example of the essvol script

alpha1> essvol
DS vol, H/W ID 176:
  phys_location = bus-9-targ-0-lun-0
  dev_base_name = dsk43
  capacity = 3906304
  serial_number = SCSI-WWID:01000010:6000-1fe1-4942-4d20-0000-0000-1042-1380

DS vol, H/W ID 225:
  phys_location = bus-9-targ-0-lun-7
  dev_base_name = dsk47
  capacity = 3906304
  serial_number = SCSI-WWID:01000010:6000-1fe1-4942-4d20-0000-0000-10a2-1380

alpha2> essvol
DS vol, H/W ID 176:
  phys_location = bus-4-targ-0-lun-0
  dev_base_name = dsk43

capacity = 3906304
  serial_number = SCSI-WWID:01000010:6000-1fe1-4942-4d20-0000-0000-1042-1380

DS vol, H/W ID 225:
  phys_location = bus-3-targ-0-lun-1
  dev_base_name = dsk47
  capacity = 3906304
  serial_number = SCSI-WWID:01000010:6000-1fe1-4942-4d20-0000-0000-10a2-1380

Use the scu command to see the reservations on these devices. Figure 2 and Figure 3 show examples of what you see when you use the scu command. You can associate dsk47 on Alpha1 and Alpha2 with storage unit volume 10a-21380.

Figure 2. Example of the scu command

alpha1> scu –f /dev/rdisk/dsk47c show reservations
Persistent Reservation Header:

                  Generation Value: 49
                 Additional Length: 16

Reservation Descriptors:

                   Reservation Key: 0x30001
            Scope-Specific Address: 0
                  Reservation Type: 0x5 (Write Exclusive Registrants Only)
                 Reservation Scope: 0 (LU - full logical unit)
                     Extent Length: 0

Figure 3. Example of the scu command

alpha2> scu –f /dev/rdisk/dsk47c show reservations
Persistent Reservation Header:

                  Generation Value: 49
                 Additional Length: 16

Reservation Descriptors:

                   Reservation Key: 0x30001
            Scope-Specific Address: 0
                  Reservation Type: 0x5 (Write Exclusive Registrants Only)
                 Reservation Scope: 0 (LU - full logical unit)
                     Extent Length: 0

Each device shows 0x30001 as a reservation key. You must issue the scu command again to remove the persistent reserve using reservation key 0x30001 on each node. Tru64 places a unique reservation key on each LUN whenever the storage unit assigns the LUN. The reservation key can only be removed from that specific host to which it is assigned. Because it is not possible to tell exactly which registrant on the host holds the reservation, you must issue an scu clear command on each node in the cluster. Figure 4 shows an example of what you see when you use the scu clear command.

Figure 4. Example of the scu clear command

alpha1> scu –f /dev/rdisk/dsk47c press clear key 0x30001
alpha2> scu –f /dev/rdisk/dsk47c press clear key 0x30001

One of the two commands that you see in Figure 4 clears the persistent reserve on storage unit volume 10a-21380.

Use the scu command to check reservations. Figure 5 shows an example of what you see when you use the scu command again.

One of the two commands you see in Figure 5 clears the persistent reserves on storage unit volume 10a-21380.

Figure 5. Example of the scu command to show persistent reserves

alpha1> scu -f /dev/rdisk/dsk47c show reservations 

Persistent Reservation Header:

                  Generation Value: 50
                  Additional Length: 0
Reservation Descriptors:

Alpha2> scu -f /dev/rdisk/dsk47c show reservations

Persistent Reservation Header:

                  Generation Value: 50
                  Additional Length: 0
Reservation Descriptors:

After removing the persistent reserve from a storage unit volume, you can use it as a target LUN for FlashCopy or Remote Mirror and Copy.