# Deduplication for Commvault VTL 2.0

## Deduplication Metadata For a Storage Pool

The Default storage pool is a system defined storage pool and cannot be deleted. The Default storage pool is special in that a disk configured for the Default storage pool can hold deduplication tables for other storage pools. Each storage pool (including the default) would have a master disk. The master disk is the first disk configured for that storage pool.

A storage pool can maintain deduplication tables in its own master disk, or on the master disk of the Default storage pool. When creating a storage pool, if the Enable dedupe metadata option is selected, the storage pool will maintain its own deduplication tables. Otherwise, the master disk from the Default storage pool is used. If a storage pool depends on the Default storage pool for the data deduplication tables, then the Default storage pool needs to have a disk configured first.

There is a limit on the number of storage pools which can maintain their own deduplication tables. By default the maximum number of storage pools which can maintain the deduplication metadata is one The preferred approach is to configure a disk in the Default storage pool. The Default storage pool will then be used to maintain the deduplication tables for all other storage pools.

The number of storage pools which can maintain the deduplication metadata can be extended by the following steps:

- Add the following to /commvaultvtl/etc/commvault.conf. Create the file if it does not exist

      SequentialTables=0

- Restart the services:

      service commvaultvtl restart

If more than one storage pools needs to maintain its own deduplication metadata, `SequentialTables=0` must be set in `commvault.conf` prior to adding any disk to any of the storage storage pools.

## Impact of Storage pools on Deduplication

- Storage pools have a significant impact on deduplication ratio.

- Data within a specific storage pool is deduplicated. For example, if 2 cartridges, V1 and V2 for example, are configured in the system, with V1 belonging to storage pool A and V2 belonging to storage pool B. If V1 receives data identical to that on V2, the data cannot be deduplicated as V1 and V2 belong to different storage pools.

### Listing Deduplication Statistics in Currently Configured Storage Pools

1. From the navigation pane, click Storage Pools.

   The Configured Pools page appears.

   The Disks column indicates the number of physical disks configured for the Storage pool.

2. In the Details columns for a configured storage pool, click View.

   For storage pools that are deduplicated, the statistics is displayed under Pool Disk Statistics.

   - Total Size is the cumulative usable capacity of all disks configured in the storage pool.

   - Used Size is the cumulative capacity used.

   - VCartridge Usage is the capacity used for cartridge data and metadata. (Used Size - VCartridge Usage) is therefore the capacity used for other metadata such as deduplication tables, the disk metadata, and so on.

   - Deduped Size is the size of duplicate data found.

   - Uncompressed Size is the size of data which cannot be compressed and written as is to disk.

   - Compressed Size is the size of data on disk which corresponds to compressed data.

   - Compression Hits corresponds to the original size of data. Therefore (Compression Hits / Compressed Size) equals the compression ratio.

   - Dedupe Ratio is calculated as (Uncompressed Size + Compression Hits + Deduped Size) / (Uncompressed Size + Compressed Size). This is equal to (vcartridge data received from the host / size of data on disk).

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