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Description of RAID 5 - Independent Access Arrays

In RAID 5, the redundancy offered in RAID 3 by a single parity disk, is distributed across all the disks in the array. Data and relative parity are never stored on the same disk. One user may be writing a chunk to disk 0 and the corresponding parity to disk 3, another user may be writing to chunk 4 of disk 1 and updating parity on disk 2. There is a clear dividend in terms of performance and the speed of transactions. During disk writes, RAID 5 cannot produce a write performance comparable to that of straight disk striping because other operations have to be undertaken to make and store parity codes. The I/O performance of the array depends very much on the relative levels of reads and writes requested. When a stripe is modified, unmodified portions must also be read to re-generate the parity for the entire stripe. Once the parity has been generated, the modified data and parity information must be written to disk. This is commonly know as Read/Modify/Write strategy. It reflects that, though RAID 5 is superior to RAID 0 because it offers redundancy, it is not able to perform as well as RAID 0 in terms of write performance. Because RAID 5 has distributed parity, two reads and two writes must be performed for every write operation. However, the write penalty can be overcome by the use of write caching which allows write data to be stored in the memory prior to writing to the disk, so freeing the host processor for other tasks. Summary: RAID 5 is ideal for organizations running databases and other transaction-based applications such as: banks, airline and railway reservation systems, government departments, utilities and telecommunications.*


HARD DISK DRIVES

EIDE and IDE drives using 2.5" laptop and 3.5" Normal 40 pin ATA through Ultra ATA/66 interfaces from all manufacturers including:

Areal, CDC, Compaq, Conner, Digital, Fuji, Fujitsu, Hitachi, IBM, Imprimis, Integral Peripherals, JTS, JVC, Kalok, Maxtor, Micropolis, Miniscribe, NEC, Plus, Priam, Quantum, Samsung, Seagate, TEAC, Toshiba, Western Digital, Xebec.

SCSI drives using Normal SE, UW, Differential (WD), LVD, Hot Swappable (SCA) and 2.5" laptop interfaces from all manufacturers including:

CDC, Compaq, Conner, Digital, Epson, Fujitsu, Hitachi, Hewlett-Packard, IBM, Imprimis, Maxtor, Micropolis, NEC, Quantum, Rodime, Samsung, Seagate, Toshiba, Western Digital.

ESDI, RLL and ST/MFM drives from all manufacturers including: Conner, Digital, Fuji, Fujitsu, IBM, JTS, Kalok, Kyocera, LaPine, Maxtor, Micropolis, Microscience, Miniscribe, NEC, Priam, Quantum, Seagate, Tandon, Toshiba, Tulin, Western Digital.

MCA drives from IBM, Western Digital and Seagate with IBM ST-506 and ESDI and 2.5" laptop ESDI interfaces.

PCMCIA Type I, II, III hard drives from IBM, Western Digital, Integral Peripherals and Procomm.

CF+ Type II IBM Microdrives

REMOVABLE MEDIA

Diskettes in 3.5" format with 720Kb and 1.44Mb, 5.25" format single and double sided to 1.2Mb capacity.

CD ROM, CD R/W and DVD R/W disks.

ISO Optical Formats 3.5": 128Mb, 230Mb and 640Mb, 5.25": 1.0Gb, 1.2Gb, 2.3Gb, 2.6Gb WORM and R/W cartridges, including multi-cartridge Jukebox storage systems.

Panasonic Optical 1.5Gb

Pinnacle Optical 4.6Gb

Imation SuperDisks 120Mb

Iomega ZIP disks 100Mb and 250Mb

Bernoulli 44Mb, 90Mb, 105Mb & 150Mb 5.25" cartridges, JAZZ 1Gb and 2Gb

Syquest 5.25" cartridges 44Mb, 88Mb and 200Mb, 3.5" cartridges 135Mb, 230Mb and 270Mb

SPARQ 1.0Gb and SYJET 1.5Gb cartridges, ORB 2.2Gb cartridges

ATA and SRAM Flashcards such as SmartMedia and CompactFlash

TAPES

4mm DAT format including DDS, DDS-2 and DDS-3 tapes up to 24Gb capacity.

8mm Exabyte Digital tape including 112m and 160m tapes.

Quantum DLT III and DLT IV tapes up to 80Gb capacity.

Seagate AIT tapes up to 50GB capacity.

OnStream ADR tapes up to 50Gb capacity.

Travan TR-4 8Gb QIC tapes.

Iomega Ditto 2Gb QIC tapes.

QIC DC600 series tapes up to 4Gb capacity.

QIC Mini-Cartridges DC2000-DC2120 with 40 to 80Mb capacity.

OPERATING SYSTEMS AND FILE SYSTEMS

INTEL PLATFORMS

Windows 2000 Professional and Server with NTFS, FAT32 or FAT16 file systems using standalone, spanned, striped or fault-tolerant RAID volumes.

Windows NT Workstation and Server with NTFS or FAT16 file systems using standalone, spanned, striped or fault-tolerant RAID volumes.

Windows 98/95 with FAT32 or FAT16 file systems and long filenames.

MS-DOS and variants using 12 or 16 bit FAT file systems.

Compressed volume managers including Stacker, DoubleSpace, and DriveSpace.

OS/2 with FAT and HPFS file systems.

Novell NetWare with FAT and NSS files systems using standalone, spanned, striped or fault-tolerant (RAID) volumes.

UNIX OPERATING SYSTEMS

SCO OpenServer and Xenix
UnixWare from Novell & SCO
Solaris
Linux (all distributions)
BSDI
FreeBSD
QNX

NON-INTEL PLATFORMS

Apple Macintosh with HFS and HFS+ file systems, including fault-tolerant (RAID) volumes.

Solaris on Sun/SPARC workstations including fault-tolerant (RAID) volumes.
HP-UX on Hewlett-Packard workstations including LVM volumes.
IRIX on SGI workstations.
AIX on IBM RS/6000 workstations including LVM volumes

*Content source www.gtweb.net.