Configure the Virtual I/O Server to support SCSI-2 reserve functions

Understand the virtual SCSI setup requirements to support applications using SCSI reserve and release.

Virtual I/O Server versions 1.3 and later provide support for applications that are enabled to use SCSI-2 reserve functions that are controlled by the client logical partition. Typically, SCSI reserve and release is used in clustered environments where contention for SCSI disk resources might require greater control. To ensure that Virtual I/O Server supports these environments, configure the Virtual I/O Server to support SCSI-2 reserve and release. If the applications you are using provide information about the policy to use for the SCSI-2 reserve functions on the client logical partition, follow those procedures for setting the reserve policy.

Complete the following tasks to configure the Virtual I/O Server to support SCSI-2 reserve environments:

Configure the Virtual I/O Server reserve_policy for single_path, using the following command:
```
chdev -dev1 hdiskN -attr reserve_policy=single_path
```
Note: Perform this task when the device is not in use. If you run this command while the device is open or in use, then you must use the -perm flag with this command. If you use the -perm flag, the changes do not take effect until the device is unconfigured and reconfigured.
Configure the client_reserve feature on the Virtual I/O Server.
- If you are creating a virtual target device, use the following command:
```
mkvdev -vdev hdiskN -vadapter vhostN -attr client_reserve=yes
```
  where hdiskN is the virtual target device name and vhostN is the virtual SCSI server adapter name.
- If the virtual target device has already been created, use the following command:
```
chdev -dev vtscsiN -attr client_reserve=yes
```
  where vtscsiN is the virtual device name.
On the Virtual client, complete the following steps to configure the SCSI reserve and release support for the virtual disk backed by the physical disk that you configured in step 1:
1. Set the reserve policy on the Virtual client to single_path, using the following command:
```
chdev -a reserve_policy=single_path -1 hdiskN
```
  where hdiskN is the virtual disk name
  Note: Perform this task when the device is not in use. If you run this command while the device is open or in use, then you must use the -p flag. In that case, the changes do not take effect until the device is unconfigured and reconfigured.
2. Set the hcheck_cmd attribute so that the MPIO code uses the inquiry option. If the hcheck_cmd attribute is set to test unit ready and the backing device is reserved, then test unit ready will fail and log an error on the client.
```
chdev -a hcheck_cmd=inquiry -1 hdiskN
```
  where hdiskN is the virtual disk name.

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Last updated: Thu, June 12, 2014