Avoid RAID 5 servers

Well, you will hate me once again, but I need to tell you this. Whoever tells you RAID 5 is a great thing on their servers, run away and do not look back.



I do not know how many tech guys we have here, but if you are one of them, read below:

[url]http://www.miracleas.com/BAARF/1.Millsap2000.01.03-RAID5.pdf[/url]



When understood, join the group here:

[url]http://www.baarf.com/[/url]



I yes, I’m on RAID 1. Yeah!

I’m not fond of raid 5 and won’t use it for heavy write intensive services but it is still the most popular and widely used for data storage/retention.



This is a pretty good sheet explaining different raid options and their uses



[url]http://www.adaptec.com/en-US/_common/compatibility/_education/RAID_level_compar_wp.htm[/url]

Article is biased and leaves out the important point that the parallelism achieved by RAID5 is superior to RAID1. The down side is that for each disk write to complete, the parity info must be written to the parity disk. This gives you a small write penalty for RAID5 over RAID1. But note, that if you do loose a disk, you will have to create the mirrored image in RAID1 before you can continue to operate in a live environement with mirrored protection. In RAID5, ti will be recreated from the parity disk as bandwidth is available. So is is a higher reliability solution!



The other factor is that RAID5 supports “stripping” which means that a write of several disk blocks can be written in parallel to multiple disks. RAID1 does not support stripping, only mirroring. So the performance penallty for RAID5 related to having to write to the parity disk (single path) can be offset by the parallelism achieved by stripping. But this all depends on the average wriite size of the system.

Myself, I always recommend RAID 1 for small servers and yes, you can continue working while one of the hard drives [after failure and replacement] is being mirrored. It takes longer to access shared docs over the network, but in overall it’s OK.



Depending on the controller and software you use, you can also schedule mirroring for later - out of business hours. This is not available in Server 2000 or 2003. No clue about 2008. Hot swap makes things even easier and better. No point to bring it down.



Having recently a server to set up with 4xHDDs, I decided to go with RAID10. Capacity wise, one HDD is lost when in RAID10 however, with MS Exchange, Sharepoint, DFS and AD + 40 something users, this was the best configuration to achieve a good performance and data protection.



And I will keep things that way.