In LU-DPU, Lazy Updates runs at read-only sites and Diligent Priority Updates runs at cluster head of the read-write sites.
In the cluster head of read-write site, LU-DPU and LDU-DPU protocol works in the same manner.
The experiment setup is done on thirty virtual machines out of which fifteen are reserved for the read-only sites and the rest used for the cluster of read-write sites.
Putting the read-write heads as close as possible to the disk surface allows high bit densities.
But as data densities increase to, say, 25,000 tracks per inch - the estimated capacity around the year 2001 - the width from track to track decreases to less than a micron, and the read-write head's position accuracy must be within 100 nanometers.
To speed data access time, engineers try to reduce the duration of beam settling, a period when the beam's and the read-write head's vibrations are dying down.
Theoretically, the distance between the disk and the read-write head never changes.
They are borrowing an idea from optical disk-drive manufacturing, in which a piggyback-style dual-stage actuator moves the read-write head through micron-level distances to reduce tracking errors.
The micromotor fits between the read-write head/slider bearing assembly and the stainless steel load beam.
Current 2-gigabyte-capacity disk drives that are part of Sun workstations and Hewlett-Packard RISC stations, for example, use 10 storage disks and 20 read-write heads within a package about 2 inches thick.