Creating data reduction pools

To use data reduction technologies on the system, you need to create a data reduction pool, create thin-provisioned or compressed volumes, and map these volumes to hosts that support SCSI unmap commands.

Data reduction can increase storage efficiency and performance and reduce storage costs, especially for flash storage. Data reduction reduces the amount of data that is stored on external storage systems and internal drives by reclaiming previously used storage resources that are no longer needed by host systems. To estimate potential capacity savings that data reduction technologies can provide on the system, use the Data Reduction Estimator Tool (DRET). This tool analyzes existing user workloads which are being migrated to a new system. The tool scans target workloads on all attached storage arrays, consolidates these results, and generates an estimate of potential data reduction savings for the entire system.

Go to https://www-945.ibm.com/support/fixcentral/ to find the tool and its readme. Data reduction is only supported Lenovo Storage V5030 and Lenovo Storage V5030F systems.

The system supports data reduction pools, which can contain thin-provisioned or compressed volumes. Data reduction pools also support additional capacity savings on thin-provisioned and compressed volumes by supporting data deduplication. When deduplication is specified for a thin-provisioned or compressed volume, duplicate versions of data are eliminated and not written to storage, thus saving additional capacity. Data reduction pools also contain specific volumes that track when space is freed from hosts and possible unused capacity that can be collected and reused within the storage pool. When space is freed from hosts, the process is called unmapping. Unmap is a set of SCSI commands that hosts use to indicate that allocated capacity is no longer required on a target volume. The freed space can be collected and reused on the system without the reallocation of capacity on the storage. The pool can also reclaim unused capacity in a data reduction pool and redistribute it to free extents. Reclaimable capacity is unused capacity that is created when data is overwritten, volumes are deleted, or when data is marked as unneeded by a host by using the SCSI unmap command. When a host no longer needs the data that is stored on a volume, the host system using SCSI unmap commands to release that storage from the volume. When these volumes are in data reduction pools, that space becomes reclaimable capacity and is monitored and collected and eventually redistributed back to the pool for use by the system. In the management GUI, reclaimable capacity is added to the available capacity for the data reduction pool. For standard pools, available capacity does not include any reclaimable capacity. In the command line interface, lsmdiskgrp command displays the different values that apply to data reduction and standard pools. For data reduction pools, the value for reclaimable_capacity indicates the amount of unused capacity that is available after data is reduced in the pool. Unlike with the management GUI, reclaimable_capacity is not included in the free_capacity value that is displayed in the lsmdiskgrp. Reclaimable capacity is collected as metadata and is also stored in the data reduction pool, thus using storage on the external storage system. The system periodically returns this capacity back to the pool, however, the system can use up 85% of the available logical capacity with reclaimable data, which can generate out-of-space warnings on the external storage system incorrectly. When creating data reduction pools, ensure that 15% of the total capacity that is allocated is reserved for these operations. Reclaimable capacity can be used for other volumes, which more efficiently uses existing storage resources. Monitor physical capacity of data reduction pools in the management GUI by selecting Pools > Pools. In the command-line interface, use the lsmdiskgrp command to display the physical capacity of a data reduction pool.

Support for the host SCSI unmap command is disabled by default. To enable support for a host to use SCSI unmap commands, enter the following command:

chsystem -hostunmap on

Using the management GUI

To create data reduction on the system, complete these steps:

Create a data reduction pool by completing these steps:
1. In the management GUI, select Pools > Pools.
2. On the Pools page, click Create.
3. On the Create Pool page, enter a name of the pool and select Data Reduction.
4. Click Create. Data reduction pools are created as parent pools only, not child pools.
Add storage to the data reduction pool by completing these steps:
1. In the management GUI, select Pools > Pools.
2. Right-click the data reduction pool that you created and select Add Storage.
3. Select from the available storage and allocate capacity to the pool. Click Assign.
Create compressed, thin-provisioned, deduplicated, or a combination of these volumes in the data reduction pool and map them to hosts by completing these steps:
1. In the management GUI, select Volumes > Volumes.
2. On the Volumes page, click Create Volumes.
3. On the Create Volume page, select the type of volume that you want to create.
4. Enter the following information for the volume:
  Pool
  
  Select a data reduction pool from the list. Compressed, thin-provisioned, and deduplicated volumes and copies must be in data reduction pools.
  
  Volume details
  
  Enter the quantity, capacity, and name for the volume or volumes that you are creating.
  
  Capacity savings
  
  Select either None, Thin-provisioning, or Compression. For any of these options you can also select to use deduplication for the volume that you create. For example, you can create a compressed volume that also uses deduplication to remove duplicate data.
  Note: If your system contains self-compressed drives, ensure that the volume is created with compression enabled. If not, the system cannot calculate accurate available physical capacity.
5. Click Create and Map.
  Note: Select Create to create the volumes in the data reduction pool without mapping to hosts. If you want to map volumes to hosts later, select Hosts > Hosts > Add Hosts.
6. On the Create Mapping page, select Host to display all hosts that are available for mapping. Hosts must support SCSI unmap commands. Verify that the selected host type supports SCSI unmap commands. Click Next.
7. Verify the volume, and then click Map Volumes.

Using the command-line interface

To create data reduction on the system, complete these steps:

To create a data reduction pool, enter the following command:
```
mkmdiskgrp -name pool_name -ext extent_size -datareduction yes
```
Where pool_name is the name of the pool and extent_size is the extent size of the pool. Data reduction pools are created as parent pools only, not child pools.
To create a compressed or thin-provisioned volume within a data reduction pool, enter the following command:
```
mkvolume -name name -pool storage_pool_name -size disk_size -compressed
```
```
mkvolume -name name -pool storage_pool_name -size disk_size -thin
```
Where name is the name of the new volume, storage_pool_name is the name of the data reduction pool, and disk_size is the capacity of the volume.
To map the volume to a host, enter the following command:
```
mkvdiskhostmap -host host_namevdisk_name
```
Where host_name is the name of the host and vdisk_name is the name of the volume.