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Configure Block Size in a Blockstore


When you back up your deployment to a Blockstores, the Backup Daemon first takes a snapshot of the head database. It then breaks this snapshot into blocks and writes these blocks to the blockstore.

The different blockstores have different default sizes and ranges of sizes for blocks.

Blockstore Type Block Size Range Default Size
MongoDB 64 KB to 15 MB 64 KB
S3 64 KB to 16 MB 16 MB

You can change the block size to suit your use case.


In general, increasing block size results in faster snapshots and restores, but requires more disk space. These competing factors should be considered when determining if you wish to tune the block size.

There are two exceptions where performance improves as the block size increases without requiring additional disk space:

Workload Impact
Update- and Delete-Intensive No matter how small you make the block size, the entire block file is rewritten. Since the entire file is always rewritten, there is no difference in storage space if you change the block size.
Insert-only The existing blocks never change. As you increase block size, block management is simplified. This enables the best possible performance on snapshot and restore.



Click on the name of the replica set that you wish to edit.


Select the desired minimum block size from the drop-down menu.

The range of minimum block sizes include:

  • 64 KB
  • 128 KB
  • 256 KB
  • 512 KB
  • 1 MB
  • 2 MB
  • 4 MB
  • 8 MB
  • 15 MB (MongoDB) or 16 MB (S3)


The updated minimum block size only applies to new and updated files in future snapshots. Existing blocks are not resized.


Click Update.