Comments on: RAID vs Mirroring http://itknowledgeexchange.techtarget.com/itanswers/raid-vs-mirroring/ Wed, 22 May 2013 18:27:48 +0000 hourly 1 By: ariens72 http://itknowledgeexchange.techtarget.com/itanswers/raid-vs-mirroring/#comment-45655 ariens72 Fri, 15 Jul 2005 14:08:56 +0000 #comment-45655 I should caution you I’m not that familiar with the IBM i5 520 product line but here’s a tidbit of information which may or may not help. Review this for starters http://www.cuddletech.com/veritas/raidtheory/x31.html
Bottom line is RAID 5 will give you more disk space for the given number of disk drives. Why IBM provides the mirrored drives at lower cost would make me think they are suppling differnet drives. Lower rpm to balance the better throughput of mirroring versus RAID 5 or they are burying the cost of the RAID disk controller across the drives. Need a lot more info on type of applications being used, transactions to be processed, and uptime requirements to answer more specifically.

]]> By: poppaman2 http://itknowledgeexchange.techtarget.com/itanswers/raid-vs-mirroring/#comment-45656 poppaman2 Fri, 15 Jul 2005 08:38:15 +0000 #comment-45656 The answer to your question depends entirely on what you are trying to do with the system being configured: it takes more processing power (on the RAID card or subsystem) to process RAID 5 information (parity needs to be calculated, using an algorithm such as XOR) than it does to process RAID 1 (write 2x from cache before purging, or send the information down two “pipes” instead of one).

Benefits of RAID 1 (mirroring): virtually instantaneous recovery from a disk failure. Drawbacks: cost/loss of raw disk capacity.

Benefits of RAID 5 (striping): Somewhat faster data READS (more spindles); less loss capacity than disk mirror (RAID 1) or disk duplexing (duplication of entire I/O subsystem); cheaper to implement than RAID 5. Drawbacks: slower WRITES (unless a fairly large cache is used); longer recovery times from failure; space constraints (how many slots do you have in your enclosure?).

I have seen and used both RAID 1 and RAID 5 in a single system: RAID 1 for the OS and RAID 5 for data.

There is also (for the truly paranoid among us) RAID 1,5 (or 5,1) in which a logical drive is striped and then mirrored (5,1) or mirrored and then striped (1,5). The benefits and drawbacks should be obvious….

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