Original URL: http://www.theregister.co.uk/2009/06/25/adaptec_capacitor/

Adaptec adds NAND cache to RAID cards

Look mum, no battery back-up

By Chris Mellor

Posted in The Channel, 25th June 2009 07:02 GMT

Adaptec has done away with the need for battery back-up of its RAID controller cards by changing to a NAND flash cache and capacitor set up.

The 5 Series RAID cards have cache memory which stores data before it leaves the card. Any power failure will cause this data to be lost. The general fix for this is battery back-up which can power the card's memory cache for up to 72 hours if there's enough of it.

Adaptec's idea with its 5Z Series cards (Z standing for zero maintenance) is to use a super-capacitor instead. If power to the card fails it stores enough power to write the memory cache contents to a secondary NAND cache, preventing data loss and removing the dependency on short-term battery life.

The capacitor is a separate unit from the RAID to which it is connected by a power cord tether.

There are additional advantages to the capacitor back-up scheme. There is no lengthy recharge time as is the case with lithium ion batteries, with super-capacitors charging up in minutes after power is switched back on.

Lithium batteries can be a nuisance for distributors and the like to ship, with airlines requiring documented drop test information before allowing them on board. Lithium batteries also need to be disposed of as hazardous waste. There are no such problems with the super-capacitor alternative.

Fujitsu Siemens Computers, the old Siemens and Fujitsu joint-venture, used a capacitor scheme instead of battery back-up in its drive arrays, and for the same reasons.

Adaptec is introducing the 5Z upgrade to its low port count cards first, with the 5445Z (4 internal + 4 external ports), 5805Z (8 internal ports), and 5405Z (4 internal ports). It will progress to the higher port count products later. These three cards are shipping now and priced from $785. ®