IDE RAID Comparison

ADAPTEC AAA-UDMA

As we move to the hardware RAID solutions we got, things get infinitely more interesting. No longer does the controller consist of an IDE controller and a BIOS chip but now the cards include processing units and memory, among other items.

The AAA-UDMA is one of the few Adaptec hardware based IDE RAID solutions. As the picture of the card clearly shows, there is a lot going on. It took quite a bit digging around to find out what each chip on the AAA-UDMA does..

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Let's start off with a component that we know every IDE hardware RAID card needs: a coprocessor. For the hardware portion of the card, the AAA-UDMA makes use of Adaptec's own RAID coprocessor: the AIC-7915G. Since this chip is made by Adaptec is is proprietary to their hardware RAID solutions, not much information on the AIC-7915G is available. All we really know about this chip is that it does at least the XOR calculations needed for a RAID 5 configuration and perhaps does more (such as determining where to split and send data).

From here on out, we can find a bit of information regarding the chips on the AAA-UDMA but at first were puzzled by what function they serve. The reason is because two of the four remaining large chips are both noted as SCSI chips on venders websites. The first of the two, the qLogic FAS466 is actually a SCSI controller according to qLogic's website. The second is the Adaptec AIC-7890 chip; a chip which Adaptec's site labels a single-chip SCSI host adapter with Ultra2 SCSI support. What are these SCSI chips are doing on the card?

Well, the AAA-UDMA uses the third large chip to translate the SCSI information sent by its components into information that an IDE device can use. The chip that serves this function is the Altera Flex EPF6024 and it acts as a translator of sorts as well as the UDMA controller. With Adaptec's previous success in the SCSI RAID market, it was easier for them to design a IDE RAID card off their existing SCSI RAID technology.

The fourth large chip on the card is the Intel 21152 transparent PCI-to-PCI bridge. This bridge, which is integrated in the popular i960 coprocessor, allows for the use of the two extra IDE controllers present on the AAA-UDMA.

The AAA-UDMA does offer four IDE output ports, but each port is only capable of accepting one drive. This is done to prevent the drives from having to wait when writing information. Since a two drive channel can only read or write to one drive on the channel at a time, having support for both a master and a slave would decrease performance of the array. The four ports are provided via two IDE controllers integrated on the Alter Flex EPF6034 chip. One downside to this controller is the fact that it is only a ATA66 controller, meaning that it cannot provide ATA100 drives with the maximum amount of bandwidth they can handle.

The AAA-UDMA uses a standard 168-pin EDO DIMM for cache memory. Our card came packaged with a 2MB DIMM but the card can accept up to 64MBs of cache memory.

The card also features a set of LEDs located at the front of the board that are used for diagnostics. Also on the card are pin headers for hard drive activity LEDs.

One big complaint we had with the AAA-UDMA was that the card's BIOS did not contain any utilities to configure or create an array. Instead the card uses a bootable floppy disk to provide these functions. This turned out to be a big pain, especially when we misplaced the disk and had to download and create a new one.