Read ahead options
Ceph Block Devices support read-ahead and prefetching to optimize small, sequential reads. This is generally handled by the guest OS in the case of a virtual machine (VM), but boot loaders potentially do not issue efficient reads. Read-ahead is automatically disabled if caching is disabled.
Table 1 lists the read ahead configuration
options for Ceph Block Devices.
| Option | Description | Type | Required | Default |
|---|---|---|---|---|
rbd_readahead_trigger_requests |
Number of sequential read requests necessary to trigger read-ahead. | Integer | No | 10 |
rbd_readahead_max_bytes |
Maximum size of a read-ahead request. If zero, read-ahead is disabled. | 64-bit integer | No | 512 KiB |
rbd_readahead_disable_after_bytes |
After this many bytes are read from an RBD image, read-ahead is disabled for that image until it is closed. This allows the guest OS to take over read-ahead after it is started. If zero, read-ahead stays enabled. | 64-bit integer | No | 50 MiB |