Following Apple's calling it quits on the Xserve in January, Mac managers have by necessity been creative to fill the void. A tip shows that it's possible to build a Redundant Array of Independent Servers (RAIS) that takes advantage of the new Mac mini's ThunderBolt port and the Target Disk Mode long built into the Mac OS.
On the AFP548.com site in February, contributor Josh Wisenbaker suggested using a Mac mini RAIS as a way to increase redundancy for a low-cost server setup.
Take one Mac mini server configure as you like and enable its boot drive as a RAID member. Boot the other Mac mini server into Target Disk Mode. Connect them with a FW-800 cable (or ThunderBolt cable if the equipment supports it). Add the TDM mini to the mirror that the boot drive is in.
Target Disk Mode is a long-standing feature of the Mac that lets you connect a pair of Macs and use one as a hard drive. It's the easiest and fastest way to upgrade systems. It used to be called SCSI Disk Mode, that's how long it's been a part of the Mac.
Precursor Systems, a Mac consultancy based in Winnipeg, Manitoba, has maintained a page on the RAIS concept. Founder Alex Narvey posted on Monday that he had tested the system running Lion Server and SoftRAID 4.07 ($129), third-party Mac RAID software by the eponymous SoftRAID LLC.
In an interesting tip, Narvey suggested using the ThunderBolt port for one mirror and the FireWire 800 port for a second Target Disk Mode mirror. SoftRAID supports this.
With SoftRAID you can even add ANOTHER mirror. So if you have used the FireWire port for your TD Mac mirror you can add a USB/FW800 drive to the USB port, make it a mirror and then if one computer or the other blows up you can send it off for repair and replacement and maintain a mirror all the time just by popping that USB drive into the empty FireWire port (for best performance of course).
(With the new Thunderbolt minis your FireWire port would be available for the external drive all the time.)
Narvey compares a restore using Apple's software RAID and SoftRAID. Check it out.