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

DRAFT -- Revision 2.0
August 22, 1996Page 30
- overall performance depends entirely on workload and use of RAID 1 versus
RAID S and SRDF
- no boot support in a multi-initiator (shared bus) environment
- high cost for small configurations
- internal RAID group configuration and LUN assignment must be performed by
EMC support personnel
Solid State Disks
Solid state disks are relatively new to the marketplace. The name is really an
oxymoron. It is not a disk drive, but a disk drive replacement. The solid state disk
emulates a regular disk but uses non volatile semiconductor RAM instead of rotating
disk media. The main reason for using a solid state disk is to increase performance.
Seek time , which is the factor that most affects rotating disk performance is non
existent on a solid state disk.
Solid state disks are very expensive compared to regular disk drives. However, their
very fast access time might compensate for the increased price in performance-
sensitive situations. Several companies market solid state disks. Examples are:
Disk Emulation Systems of Santa Clara, California
Quantum Corporation of Milpitas, California
Storage Computer of Nashua, New Hampshire
One product from Disk Emulation Systems (DES) provides ECC memory, battery
backup, and automatic backup to an internal disk in case of power outage. Another
product provides transparent mirroring to disk and redundant power supplies in addition
to the previous features. Solid State disks from DES have capacities up to 4 GB.
Hardware support for DES products is provided by HP field repair personnel on all
vendors' platforms.
Advantages and disadvantages of solid state disks
Solid state disks have the following advantages and disadvantages:
+ much higher performance than any standalone disk or RAID array
+ no rotational latency
+ no seek time
+ appears to the OS as if it were a normal disk
- much higher cost
- not purchasable from HP