+ safe_mode_delay
+ When an md array has seen no write requests for a certain period
+ of time, it will be marked as 'clean'. When another write
+ request arrive, the array is marked as 'dirty' before the write
+ commenses. This is known as 'safe_mode'.
+ The 'certain period' is controlled by this file which stores the
+ period as a number of seconds. The default is 200msec (0.200).
+ Writing a value of 0 disables safemode.
+
+ array_state
+ This file contains a single word which describes the current
+ state of the array. In many cases, the state can be set by
+ writing the word for the desired state, however some states
+ cannot be explicitly set, and some transitions are not allowed.
+
+ clear
+ No devices, no size, no level
+ Writing is equivalent to STOP_ARRAY ioctl
+ inactive
+ May have some settings, but array is not active
+ all IO results in error
+ When written, doesn't tear down array, but just stops it
+ suspended (not supported yet)
+ All IO requests will block. The array can be reconfigured.
+ Writing this, if accepted, will block until array is quiessent
+ readonly
+ no resync can happen. no superblocks get written.
+ write requests fail
+ read-auto
+ like readonly, but behaves like 'clean' on a write request.
+
+ clean - no pending writes, but otherwise active.
+ When written to inactive array, starts without resync
+ If a write request arrives then
+ if metadata is known, mark 'dirty' and switch to 'active'.
+ if not known, block and switch to write-pending
+ If written to an active array that has pending writes, then fails.
+ active
+ fully active: IO and resync can be happening.
+ When written to inactive array, starts with resync
+
+ write-pending
+ clean, but writes are blocked waiting for 'active' to be written.
+
+ active-idle
+ like active, but no writes have been seen for a while (safe_mode_delay).
+
+