topic Re: Raid 5 vs Raid 3 in Disk Enclosures

Raid 5 vs Raid 3

SP.PALANIAPPAN — Fri, 24 Nov 2006 05:23:29 GMT

What is necessity of using raid 5 in case of raid 3? what is the main difference in using raid 5 instead of raid 3 ?

Re: Raid 5 vs Raid 3

raadek — Fri, 24 Nov 2006 06:32:53 GMT

RAID 3 term is very rarely used, usually people name it RAID 4.

The main difference between RAID 3/4 and RAID 5 is the fact, that the former has a dedicated drive for storing parity information, what usually creates a bottleneck. RAID 5 spreads parity info accross all drives, thus elminating this problem.

This link gives a good overview of RAID levels:
http://www.pcguide.com/ref/hdd/perf/raid/levels/single.htm

Rgda

Re: Raid 5 vs Raid 3

Ivan Ferreira — Fri, 24 Nov 2006 12:54:42 GMT

RAID 3 use a single disk for parity saving, this disk could become a bottleneck. RAID 5 uses distributed parity to avoid possible performance problems.

Re: Raid 5 vs Raid 3

Patrick Terlisten — Fri, 24 Nov 2006 13:52:27 GMT

Hello,

the main difference between the raid-levels is that RAID 3 uses a dedicated disk drive for it's parity informations, and it stripes on byte level. RAID 4 uses block striping with a dedicated parity disk and RAID 5 uses block striping and distributed parity.

RAID 3 is good for sequential read I/O (multimedia, video edit...), but it will not perform very well if you're using it for sequential write I/Os. RAID 4 is much better for this usecase, but you still have a single disk for your parity informations - and that's the bottleneck. RAID 4 and RAID 4DP is still used by NetApp for their Filers.

Regards,
Patrick