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3ware TwinStor

Architecture

™

TwinStor™ Technology: A Compelling Case for Multiple Drives in PCs, Servers and Workstations

(August 1999;November 2000; revised April 2002)

Executive Summary

3ware's TwinStor technology provides an optimized method of maintaining mirrored data on pairs of ATA disk drives.

Because twin images of the data exist – one image on each drive – backup of valuable data is essentially accomplished

each time data is written to the disks.

This safeguard would benefit many of today's computer systems, as most systems contain only a single disk drive that's

"protected" by expensive backup hardware and all too often forgotten. With the cost of storage rapidly declining, using a

TwinStor-enabled ATA RAID controller, such as 3ware's Escalade 7000 series, in conjunction with multiple ATA disk drives

is an inexpensive backup solution that's constantly at work protecting valuable data.

While the inherent fault tolerance of this approach effectively solves backup woes, its prime benefit goes beyond protecting

data: an even more compelling aspect of TwinStor is the dramatic performance boost that it also achieves while processing

mirrored data. When data is accessed, TwinStor technology employs a profile that it maintains of the disks' layout and an

accumulated heuristic history of drive accesses, to dynamically distribute data retrieval between the drives such that

movement of each disk arm is minimized – this reduces latency and facilitates streaming. Adaptive algorithms increase

performance to the extent that the sequential read bandwidth approaches that of striped (RAID 0) drives and the random

transaction rate exceeds that of striped and mirrored (RAID 1) solutions.

A TwinStor-enabled controller plus low-cost ATA drives provide improved performance and fault tolerance over a single-drive

configuration and benefit a wide range of applications in home, small office, and server environments.

Introduction

Desktop PCs and small servers are becoming increasingly critical in businesses and homes. The data stored on these

systems, from financial records to digital photographs, is often irreplaceable. Disk drive reliability is very high, but the

possibility of a drive failure does exist and it is important to make sure that the data remains secure and is not lost. There are

many different procedures for backing up data but none are entirely satisfactory. Mirroring the data to a second drive

provides an effective and less costly solution than daily back up to secondary media or remote servers.

Consumers will pay premium prices to obtain the highest frequency CPUs but system vendors have typically offered few

choices for improving I/O performance (even though many applications are more sensitive to I/O speed than CPU speed).

Now that CPU speeds have increased to levels of 1GHz and beyond, this disparity often results in a glaring I/O subsystem

bottleneck that hinders application responsiveness. There is however an opportunity to improve the performance of many

applications by combining transfer and transaction rates of multiple drives.