Sizing considerations

When mixing traditional and solid state drives using BlueStore OSDs, it is important to size the RocksDB logical volume (block.db) appropriately.

The RocksDB logical volume be no less than 4% of the block size with object, file and mixed workloads. IBM Storage Ceph supports 1% of the BlueStore block size with RocksDB and OpenStack block workloads. For example, if the block size is 1 TB for an object workload, then at a minimum, create a 40 GB RocksDB logical volume.

When not mixing drive types, there is no requirement to have a separate RocksDB logical volume. BlueStore will automatically manage the sizing of RocksDB.

BlueStore’s cache memory is used for the key-value pair metadata for RocksDB, BlueStore metadata, and object data.

Note: The BlueStore cache memory values are in addition to the memory footprint already being consumed by the OSD.

For more information, see the Sizing IBM Storage Ceph chapter, within the IBM Storage Ceph Concepts and Architecture Guide Redpaper publication.