Setting the reserve policy attributes of a device

In some configurations, you must consider the reservation policy of the device on the Virtual I/O Server (VIOS).

About this task

The following section explains the situations in which the reservation policy of the device on the VIOS is important for systems that are managed by the Hardware Management Console (HMC).

Situations where reservation policy of a device is important for HMC-managed systems

To use a Multipath I/O (MPIO) configuration at the client, none of the virtual Small Computer Serial Interface (SCSI) devices on the VIOS can reserve the virtual SCSI device. Set the reserve_policy attribute of the device to no_reserve.
For virtual SCSI devices used with Live Partition Mobility or the Suspend/Resume feature, the reserve attribute on the physical storage that is used by the mobile partition can be set as follows:
- You can set the reserve policy attribute to no_reserve.
- You can set the reserve policy attribute to pr_shared when the following products are at the following versions:
  - VIOS Version 2.1.2.0, or later
  - The physical adapters support the SCSI-3 Persistent Reserves standard
The reserve attribute must be the same on the source and destination VIOS partitions for successful partition mobility.
For PowerVM® Active Memory Sharing or Suspend/Resume features, the VIOS automatically sets the reserve attribute on the physical volume to no reserve. The VIOS performs this action when you add a paging space device to the shared memory pool.

Procedure

From a VIOS partition, list the disks (or paging space devices) to which the VIOS has access. Run the following command:
```
lsdev -type disk
```
To determine the reserve policy of a disk, run the following command, where hdiskX is the name of the disk that you identified in step 1. For example, hdisk5.
```
lsdev -dev hdiskX -attr reserve_policy
```
The results might look like the following output:
```
..
reserve_policy  no_reserve                       Reserve Policy                   True
```
Based on the information in the section Situations where reservation policy of a device is important for HMC-managed systems, you might need to change the reserve_policy so that you can use the disk in any of the described configurations.
To set the reserve_policy, run the chdev command.
For example:
```
chdev -dev hdiskX -attr reserve_policy=reservation
```
where,
- hdiskX is the name of the disk for which you want to set the reserve_policy attribute to no_reserve.
- reservation is either no_reserve or pr_shared.
Repeat this procedure from the other VIOS partition.
Requirements:
1. Although the reserve_policy attribute is an attribute of the device, each VIOS saves the value of the attribute. You must set the reserve_policy attribute from both VIOS partitions so that both VIOS partitions recognize the reserve_policy of the device.
2. For partition mobility, the reserve_policy on the destination VIOS partition must be the same as the reserve_policy on the source VIOS partition. For example, if the reserve_policy on the source VIOS partition is pr_shared, the reserve_policy on the destination VIOS partition must also be pr_shared.
3. With the PR_exclusive mode on SCSI-3 reserve, you cannot migrate from one system to another system.
4. The PR_key value for the VSCSI disks on the source system and the target system must be different.