Design Issues of Shingled Write Disk for Database

To maintain the continuing growth of bit density in magnetic recording media, the disk industry will have to change technologies. Shingled write disks are expected to be the next generation of high capacity magnetic disks and already in prototype. Shingled write technology is not disruptive at the level of disk design and manufacturing, but as shingled writes prevent updates in place, the technology is disruptive at the level of usage. It is possible to design a disk device driver or disk firmware that allows a shingled write disk to be used as a drop in replacement for traditional disks. Database implementations however have traditionally bypassed the file system and accessed the disk directly in order to achieve better performance. We discuss here adaptation of B+-trees and linear hash tables to shingled write disk to support indexed database tables and secondary indices. Our proposal is based on dividing the disk in low-capacity Random Access Zones (RAZ) and high capacity Log Access Zones (LAZ). The LAZ use the shingled disk effectively while RAZ places guard bands around each track in the zone in order to regain the capacity of in-place updates at the costs of loosing capacity.