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Temporal counters inaccuracy

  • Compression occurs during destage. Data in the write cache is not yet compressed (not reflected by the volume / filesystem "savings" field).
  • On a large system with 200TB of data, with a full cache (135GB) this is less than 0.07% inaccuracy (less for systems with more data)
  • Since data in write cache is not compressed, the host write is acknowledged without delay

Compressing pre-existing data

  • When upgrading a populated InfiniBox system to a software version that enables compression, the already-existing data is not automatically compressed
  • Moving old volumes to new compressed volumes (for example, using VMotion) compresses the data
  • This limitation will be eliminated in a later release

Writing non-compressed data on a compression-enabled dataset

The InfiniBox system may write data uncompressed for a compression-enabled dataset, if:

  • The system wrote the maximum amount of compressed data it can (for data that is highly compressible).
    This limit is not a hard number but rather calculated based on the memory consumed by the metadata. We estimate average compression up to 1:3 will not consume all the memory.
  • A specific volume / filesystem reached the ceiling compression ratio. Compression on that entity will stop to allow other entities to keep compressing more data.
  • Compression is ineffective (for example - data was encrypted by the host and doesn't compress) - the system avoids compression (reduces CPU load)

 

 

 

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