Why should my RAID-5 array hardware configuration be documented?

Our Answer:

Fully documenting the hardware configuration of your RAID-5 data storage array during initial setup, including the physical arrangement and order of connection for all component devices, especially the disk drives is within the realm of "miraculous life saving device" in the event that you lose data availability and trouble shooting advances to the point where even a single array member device has gone off line.  Following subsystem installation and functional checkout, i.e., once full operational integrity has been assured, check again to make sure that everything about device placement, connection, and switch status has been copiously documented to the point where a system operator would have no trouble putting it all back together after your complete disassembly.

Once trouble arises, with RAID-5 it is common to begin by replacing off-line drive elements, or by removing drives from their bays, swapping, otherwise moving them around, it takes only a short time to learn, much to your eventual dismay, that no one really knows exactly how the subsystem was configured last time it was working OK.  When data recovery of RAID-5 is under way, remember that when the sequence of stripe ordering for array member drives is known, often this can be determined only by an extremely tedious and time consuming process of trial and error; if there are four drives (sets of stripes) in the array, there are sixteen sequences possible, with five drives the number goes up to 25 possiblities.  Each iteration of trial or testing typically takes two to four hours.  Document, document, document!