Friday, August 3, 2012


The concept of MAID (Massive Array of Inactive Disks) has been recently introduced. It refers to a collection of low-cost SATA (or even PATA) disks drives that are not active until they are accessed. Once a disk is going to be accessed, it is activated. This results in a lower acquisition cost and a lower operation cost, owing to the reduced electrical consumption. Of course, response time is heavily increased as compared with active disks, since the typical starting time of a disk is about 10 seconds. MAID can be used wherever access time is not a key factor; for instance, a MAID can serve as a cache to a tape library or as an alternative to tapes.

Intelligent Discs
We must also discuss a proposal from University of California at Berkeley researchers. The proposal addresses making use of the intelligence embedded within today’s disks. They call the proposal Intelligent Disks.

The rationale is straightforward: as the industry migrates towards higher-level interfaces such as SCSI or FC-AL, disk drives needed to embed greater processing power, nowadays typically making use of a 32-bit microprocessor and several megabytes of memory. The suggestion is simply to move some file system or database functionality onto this microprocessor.

Clearly, there is a question of balance; during IBM’s introduction of the S/360, processors were relatively slow, and thus there was substantial pressure to off-load tasks from them. This lead to the use of intelligent disk controllers allowing disk searches to be done according to specified criteria (the interface was called CKD or ECKD). As time passed, minicomputers and early microprocessor systems became rather higher performance and cheap, driving the adoption of simple, low-cost disk interfaces such as SMD and later ESDI. These interfaces had limitations, and once more an intelligent interface, this time SCSI, was introduced to overcome them, necessitating the presence of microprocessors and memory in the disk drives themselves.
Choosing commodity low-cost processors provided much more computer power than was needed by the task, but kept costs down.

The success of this approach, however, does not rest on hardware technology but rather requires that the industry adopt the standards, that operating systems support it, and—perhaps most significantly—that the major database vendors also adopt it.

Source of Information : Elsevier Server Architectures

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