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OceanStor 2600 V3 Storage System V300R005 SmartDedupe and SmartCompression Feature Guide for Block 05

"This document describes SmartDedupe and SmartCompression features for block data services,including their working principles, application scenarios, and configuration processes."
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Working Principle

Working Principle

SmartDedupe and SmartCompression delete duplicate data and compress data respectively to reduce data redundancy and save storage space.

Related Concepts

Familiarize yourself with related concepts before using SmartDedupe and SmartCompression.
  • This determines deduplication granularity, and is identical to the block size of a thin LUN. To set the block size of a thin LUN, run create lun on the command line interface (CLI) and modify the value of parameter grain_size.
    NOTE:

    For details about how to use the create lun command, see OceanStor 2200 V3&2600 V3 Storage System V300R005 Command Reference .

  • Compression data block size: This determines compression granularity. The storage system compresses data intelligently using the block size of newly-written data in LUNs.
  • Fixed-length deduplication: The storage system deduplicates the data written into a LUN by the specified deduplication data block size.
  • Hash algorithm: This verifies the consistency of data blocks. It computes the fingerprint of a data block, which is a unique binary number with a fixed length. If the fingerprints of two data blocks are the same, the storage system considers them duplicates.
  • Byte-by-byte comparison policy: This is complementary to the hash algorithm. If two data blocks are found to have the same fingerprint, the storage system compares the data blocks byte by byte, ensuring that the deduplication is secure.
  • Deduplication metadata: This stores deduplication information, such as the fingerprints and storage locations of deduplicated data.

Deduplication

After SmartDedupe is enabled for a LUN, the OceanStor 2600 V3 storage system uses the hash algorithm to calculate the fingerprint of each new data block. It then compares these fingerprints with those of existing data blocks in the LUN. If a new fingerprint is identical to an existing one, it will be deleted and its storage location registered as that of the existing one. If the fingerprint is unique, the new data block is written to disks.

If you have not enabled either SmartDedupe or SmartCompression when you create a LUN, you cannot enable them any more after the LUN is created.

Figure 1-1 shows the deduplication process.
Figure 1-1  Deduplication process

Figure 1-2 shows the process of writing data to a storage system with SmartDedupe enabled and disabled. In this example, data blocks B and C have identical fingerprints, while data block D has a unique fingerprint.
Figure 1-2  Effects of using SmartDedupe

Compression

After SmartCompression has been enabled for LUNs, the OceanStor 2600 V3 performs inline compression.

The degree to which data is compressed depends on the specified compression policy. You can set the compression policy to either fast or deep:
  • The fast option is the default compression method. It is optimized for speed rather than space efficiency.
  • The deep option is optimized for space efficiency rather than speed.
Figure 1-3 shows the effects of the two compression policies.
Figure 1-3  Effects of compression policies

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Updated: 2018-06-04

Document ID: EDOC1000106188

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