MAID suffers from lack of a real volume management system and a real file system
MAID could be made more successful if it was packaged with a real volume management and file system management system, like open-source ZFS.
- The concern about disks not spinning up could be resolved with RAIDZ2 or RAIDZ3 (where 2 or 3 extra parity disks could be available)
- The concerns about the occasional I/O having to spin up all the drives for odd-writes or keeping D-R locations in-sync could be resolved with a ZFS intent log (with a very large cache.)
- A real file system and volume manager could be tuned to deal with delaying writes to disk (as long as the writes were committed to intent log in NVRAM) for hours, ensuring power savings.
- The concerns about the extra power required to spin up the disks could be resolved with super capacitors to deliver the spikes of power needed with spindowns, smoothing out the need to have huge power supplies (running inefficiently), to deal with the power spikes.
- having huge volumes, which can extend [virtually] indefinitely with ZFS, would make MAID more appealing, since splitting data-sets over [sequentially accessed] tapes and [randomly accessed] standard file systems would go away, making the media more appealing in large scale deployments
- pushing the logic to spinning down the drives into the file system / volume manager like ZFS with MAID could make the technology go mainstream, since the capabilities would not require human intervention (with the exception of specifying whether the MAID caching algorithm would need to be mild, medium, or aggressive) - but this would not do too well with proprietary hardware vendors pushing MAID now.
I am sure there is a counter argument from MAID vendors for each of these points - perhaps people in the mainstream are just not convinced they have all been addressed, yet.
Some Sun customers have been hacking together their own code to do it, at the Solaris level, instead of the ZFS level.
I have personally been using external 1.5 TB drives on a SPARC server, which spin down automatically, under ZFS with RAID. I am personally very happy with the results (far superior to when I tried to run these drives under MacOSX or Windows.) I have been considering expanding the usage after designing/implementing a better power supply which combines batteries to eliminate multiple transformers plugged into a UPS.
I love the concept of MAID, I think MAID may be just too immature right now, or just too little too late.