Caching storage data in virtual mode

In the virtual mode, the cache device is assigned to the Virtual I/O Server (VIOS).

In the virtual mode, the cache pool is created on the VIOS. The cache pool is then split into partitions on the VIOS. Each cache partition can be assigned to a virtual host (vhost) adapter. When the cache partition is discovered on the AIX® logical partition (LPAR), the cache partition can be used for caching the target device. The cache partition can be migrated to another server because the cache device is virtual. Before the migration, the caching is automatically stopped on the source LPAR. As a part of the migration operation, a cache partition of the same size is created dynamically on the target VIOS if the caching software is installed and a cache pool is available on the target VIOS. During the migration, the cache partition is made available to the LPAR. When the migration is completed, caching is automatically started on the destination LPAR. In this case, the caching starts in an empty (unpopulated) state.

The following figure shows an example of caching configuration in virtual mode, where the cache device is on a VIOS LPAR and the target device is on an AIX LPAR.

In the virtual mode, the cache device is assigned to the Virtual I/O Server (VIOS). — Figure 1. Storage data caching: Configuration for virtual cache device

Consider the cache devices are hdisk1, hdisk2, and hdisk3 (on VIOS LPAR), and the target device are hdisk4 and hdisk5 (on AIX LPAR). To start and monitor the caching of the target devices, complete the following procedure:

In the VIOS LPAR, create a cache pool by using the SSD storage.
```
# cache_mgt pool create -d hdisk1,hdisk2,hdisk3 -p cmpool0
```
In the VIOS LPAR, create a cache partition of 80 MB from the cache pool.
```
# cache_mgt partition create -p cmpool0 -s 80M -P part1
```
In the VIOS LPAR, assign the partition to a virtual host adapter.
```
# cache_mgt partition assign -P part1 -v vhost0
```

In the AIX LPAR, assign the cache partition to a target devices.

# cache_mgt partition assign -t hdisk4 -P cachedisk0
# cache_mgt partition assign -t hdisk5 -P cachedisk0

In the AIX LPAR, start caching of the target devices.

# cache_mgt cache start -t hdisk4
# cache_mgt cache start -t hdisk5

In the AIX LPAR, monitor statistics on cache hits.
```
# cache_mgt monitor get -h -s
```