Fast writes can be configured: at the controller level, in which case fast writes are set for all drives in the SPARCstorage Array; at the tray level, affecting all drives in a single tray; or at the drive level, setting fast write for that individual drive.
When fast write is enabled, it is saved as part of the SPARCstorage Array's configuration--across power cycles.
If the NVRAM battery is low, missing, or has failed, the menus will be disabled, because fast write is disabled on the controller under these conditions.
Before enabling fast write, quiesce all I/O to the controller, tray, or disk. Be sure that no I/O is active on metadevices that exist on disks within a SPARCstorage Array. In particular, insure that ownership of any diskset metadevices has been released since an implicit I/O stream exists while ownership of a diskset is maintained. Refer to "Working With Disksets" for details of taking and releasing ownership of a diskset.