NAS file systems were traditionally formatted with enhanced bitmap resiliency to provide a greater chance of recovering from defects in a storage subsystem. In general, a free space bitmap with enhanced resiliency provides a greater chance of recovery from system errors; however, some systems, such as those using HDP storage, do not benefit from enhanced bitmap resiliency. Formatting them with standard bitmap resiliency can offer a performance advantage––the average number of back-end write operations is reduced from ~6 to ~2, for each client write.
With version 12.6 and later, all file systems are formatted by default:
- With standard bitmap resiliency on HDP storage
- With enhanced bitmap resiliency on non-HDP storage
There is no special configuration needed to use this feature. File systems on HDP storage are automatically formatted with standard bitmap resiliency. Files on non-HDP storage are formatted with enhanced bitmap resiliency as before.
Two commands are provided to perform bitmap resiliency conversion:
When converting a file system from a resilient to standard format (or vice versa), note that:
- The file system must be unmounted before converting bitmap resiliency.
- Bitmap resiliency is reversible. You can undo the conversion by running one of the commands mentioned above.
- If the bitmap resiliency conversion fails, such as due to a power failure, the file system reverts to its state before the command was initiated, as if the command were never run. The file system is unchanged if the conversion fails.
- To use the fs-convert-to-enhanced-bitmap-resiliency command, the free space needed is about 8 times the data length of the free space bitmap. For the fs-convert-to-standard-bitmap-resiliency command, it is about 4 times.