Overview

Flexible tier pools (flex pools)

Flex pools are used to manage the flexible tier volumes. They consist of two or three flexible tier subpools with the performance classes "high", "middle" (optional depending on the tiering policies) and "low".

Flexible tier subpools (flex subpools)

Flex subpools correspond to thin provisioned RAID groups whose total storage is available for Automated Storage Tiering. The RAID levels of the flex subpools which are supported are RAID 1, RAID 1+0, RAID 5 and RAID 6. The flex subpools use the same drive technology (SSD, SAS or NL-SAS).

Flexible tier volumes (flex volumes)

Flex volumes are generated volumes in a flex subpool. They can be seen and addressed by the servers as "normal" volumes. During configuration the flex volumes are assigned to a flex subpool.

Tiering policies

Tiering policies are definable migration rules for Automated Storage Tiering. They define whether, how and when data migration is started. The definition and implementation of the tiering policies take place in the storage system with the management software ETERNUS SF. Monitoring and data migration are based on the I/O values measured per sub LUN.

Monitoring the flex pools

Two threshold values are set on the storage system for each flex pool to monitor the storage space consumption of the various flex pools. These are set when the flex pools are generated and cannot be modified during operation:

• ATTENTION: 75% (default value) of the flex pool's available capacity has been used

• WARNING: 90% (default value) of the flex pool's available capacity has been used

When the load on the flex pool is 100%, writes to areas which have already been allocated are still executed, but writes which require a new area are rejected with an error. The BS2000 volume is assigned the REMOUNT state.
SHC-OSD reports when each monitored flex pool reaches the threshold values and also reports its current status. Monitoring by SHC-OSD can be set, see the FLEX-POOL-MONITORING parameter in section "Configuration of SHC-OSD".

Configuration of the storage system for AST

Automated Storage Tiering is configured in the storage system by a qualified technician using the management software ETERNUS SF.

The following steps are required (for details, refer to the documentation on ETERNUS DX/AF and ETERNUS SF):

1. Enter the license for the "Thin Provisioning Feature"

2. Switch on the Automated Storage Tiering function

3. Generate the flex pool from one or more RAID groups

4. Generate flex subpools within a flex pool

5. Generate flex volumes in the flex subpools

6. Define the tiering policies

7. Set the monitoring threshold values for each flex pool

8. Dynamic extension of the flex pools (when required)When more storage is required for existing or future flex pools, existing flex pools can also be extended dynamically by additional physical devices. This extension takes place without interrupting any application which is executing.

Automated Storage Tiering and replication functions

The following combinations of flex pools and replications are supported:

• EC/QuickOPC: Replication from flex volumes to flex volumes

• REC: Replication from flex volumes to flex volumes

• SnapOPC+: Replication of flex volumes to flex volumes or snap data volumes

In the case of EC, QuickOPC and REC, flex volumes and normal volumes can be combined. However, this is not recommended as the advantage of Automated Storage Tiering is then lost.