The SPS are Standby Power Supplies; essentially a USP which, in the event of a power failure, will supply the first enclosure of the array power so that uncommitted writes can be saved to the vault drives, followed by an orderly shutdown of the controllers.  Then when the unit is restarted those changes will be read from the vault and written to the proper disks.  The reason that write cache disabled is that, without the SPS, simply copying writes to the RAM in the other SP is not sufficient to guarantee that they will ultimately committed to disk.  A power failure without SPS would lose unwritten data, corrupting any LUNs which had unwritten changes at the time of the failure.   Without write cache writes will not be acknowledged to a host until they have been physically written to the disks in the array.  That alone means that writes which are usually acknowledged at the speed of RAM are now hundreds to thousands of times slower.  If the unit is no longer under maintenance I would suggest looking for a provider of 'refurbished' SPS units.  I have replaced several where I work; they usually cost under $400, and come with a 1 year warranty.  Look for someplace that says that they are rebuilt/refurbished rather than just working pulls.  These are batteries, and they have a relatively finite lifespan.
Have an inherited a Dell-branded, EOL AX4-5 at a remote site which is reporting that both SPS's A & B have failed. [IMAGE] We have a spare one of these: [IMAGE] But am thinking this must be a Power Cooling module and not an SPS?  I can't click on the SPS failures above so I'm not even sure if these are field replaceable or not?  Can anyone give me some pointers?  Reading through manuals as well of course.
AX4-5 Standby Power Supplies Failed