drive level write caching to be enabled, for devices that
support write barriers.
+ discard
+ Issue command to let the block device reclaim space freed by the
+ filesystem. This is useful for SSD devices, thinly provisioned
+ LUNs and virtual machine images, but may have a performance
+ impact. This option is incompatible with the nodelaylog option.
+
dmapi
Enable the DMAPI (Data Management API) event callouts.
Use with the "mtpt" option.