LogDevice has this concept of "node set", which is the set of storage nodes that can be selected by the sequencer as recipients for a record or a block of records. A typical node set size is around 20-30 in our deployments. Each storage node in the node set contains a subset of the records (or blocks of records) of the log, we call that subset a log strand. The amount of IO capacity available to append records to a log or read records from a log scales with the size of the node set.

All of this is done while preserving the total ordering guarantee thanks the separation of sequencing and storage.

The operator could for example set a bigger node set size for logs that are known to have multiple consumers and require more IO capacity.

At facebook, we have use cases where a single consumer will need to replay a backlog of records in a log, sometimes hours or days worth of data to rebuild its state. We call this a backfill. Node sets allow the IO to be spread across multiple disks which improves backfill speed and helps reduce hotspots.

-- Adrien from the LogDevice team.