RAID level comparison: data protection vs. redundancy
With respect to the tradeoff between redundancy vs. data protection, what recommendations can you make on RAID levels? Is it completely dependent on the environment, or are there clear advantages to using a RAID 5 over RAID 3, etc.?
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ASKED:
January 27, 2010 9:08 PM
UPDATED:
January 29, 2010 1:23 AM
Answer Wiki:
I prefer to use RAID 10 where capacity requirements will permit me to. RAID 10 has better performance and redundancy when compaired to RAID 5, making it the ideal RAID level for mission critical applications. RAID 5 will pass if I need more storage space for lower priority applications.
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When selecting the RAID level to use you need to put the amount of cache into the equation. When everything is planning out and sized correctly you should never actually be writing to disk. All writes should go to cache. If you are writing directly to disk then you have a cache sizing issue which needs to be addressed.
As you are no longer writing to disk, can your disks in a RAID 5 config keep up with the write requests from the cache? If so then RAID 5 will suit you better as you get more disks available for reading. If redundancy is an issue look at RAID 6 as you get a double parity and can survive ANY two disks failing.
In a RAID 10 (or 1+0) you can survive any two disks failing, so long as they aren’t part of the same pair.
If a RAID 0+1 you can survive any two disks failing, so long as they are part of the same RAID 0 segment.
If in a RAID 10 (or 1+0) you loose both disks in a pair the array has failed. If in a RAID 0+1 you loose one disk in each RAID 0 segment then the array has failed.