Write Intensive Applications with RAID

[insania]

Please accept my apologies if I'm posting to the wrong forum.

Hi all,

I was wondering if there is a particular RAID level that should not be used for read/write intensive applications. Although I have done some of my own research, RAID 0+1 seems to be the best option, however I am not a network/RAID specialist and would like an expert opinion.

Also are there any key areas on how to tweak RAID servers for performance reasons i.e. reduce caching etc.

Much appreciated if any help could be provided.

Thanks

Mez

 

[technome]

You are probably referring to the industries definition of raid 10, mirrors striped, you do not want raid 01, stripes mirrored. Lately this is confusing as Dell decided to reverse the definition.
Raid 01 allows only 1 drive failure under any circumstance, r10 allows a minimum of 1 failed drive.. on raid 10, a complete group of drives on one of the mirrors could fail with no data loss, best to search google on raid 10, as this is a simplified explanation of raid 10 redundancy.

With write intense disk I/O you want raid 1 at minimum, raid 10 is faster at 4 disks, even faster with 6. with write intensive I/O, raid 5 would be a poor choice. With read intensive I/O, raid 1, r10 and r5 are all good, raid 5 can have remarkable read benchmarks. Keep in mind most "general use" servers read approx. 80% of the time, so even raid 5 does quite well overall.
To sum it up, if you are sure you have applications which are very write intensive go with a raid 10, (2 channel card, drives divided evenly over the two channels) preferably with more than 4 drives. With a server apps which really push I/O, use 15k drives. If you have the resources raid 10 is the way to go; the most disks you have in the array the more need for a hotspare disk.

Raid tuning...very little can be tuned, unless you have a server dedicated for a particular application which has data chunks which are a particular size, such as a database app. Raid 5 needs "write back" caching or performance is pitifully dismal.

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