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Hitachi Vantara Knowledge

Standard bitmap support

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
NoteStandard bitmap formatting is only supported on WFS-2 file systems. Additionally, versions 12.5 or earlier do not support standard bitmap resiliency; therefore, before downgrading to version 12.5 or earlier, all file systems with standard bitmap resiliency must be converted to enhanced bitmap resiliency, or they will not mount correctly after the downgrade.

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.


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