Choosing the Right Disk Technology in a High Availability Environment DRAFT Version 2.0, August 1996

DRAFT -- Revision 2.0
August 22, 1996Page 5
This Whitepaper will attempt to remove some of the mystery associated with various
disk technologies and will discuss the advantages and disadvantages of each, with the
goal being an easy-to-use roadmap for choosing the right disk technology.
This Whitepaper is divided into six major sections:
Disk Link Technology Comparisons
Types of Disks
Capacities
Performance Comparisons
High Availability Considerations
Decision Criteria
After first discussing the different links used with disk drives, a comparison between
standalone disks and disk arrays will be made. Then, there will be a discussion of
capacity limitations and performance issues. These five sections provide background
information needed to use the decision criteria for selecting the disk technology most
appropriate to a given situation.
Disk Link Technology Comparisons
HP has three different disk link technologies currently available:
HP-FL (Fiber Link)
SCSI (Small Computer System Interface)
Fibre Channel
HP-FL disk links
HP-FL is an HP proprietary link developed as a higher-speed alternative to HP-IB, an
older disk link technology. Disk drives are the only devices available that use HP-FL.
HP-FL uses a dual fiber optic link between the computer interface and the first disk
drive in the chain. This fiber can be as long as 500 meters, providing flexibility in the
placement of disk drives for environmental, security and high availability reasons.
SCSI disk links
SCSI is a "standard" link that was initially developed for Personal Computers. It has
been adopted by Unix workstation and server vendors to connect disk drives and many
other devices such as 4 and 8 mm tapes, scanners and CD-ROM drives.