RAID 5+1 and BAARF

I am more on the development side, so I have very little experience with 
hardware. I have read the articles on BAARF. I directly our infrastructure guy 
to the webpage and he is looking at it. Here is an email I got from him. Is 
there ever a cause to use RAID 5? 

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Using RAID1 or RAID10 would increase the cost of the company SAN by atleast a 
factor of 3.
 
I worked on this two years ago, so the information below is 2 years old.
 
In SAN  (EMC or Hitachi arrays) the issues pointed out by Milsap and others are 
avoided as follows, keeping the cost low:
 
- There are spare disks on the array. The array takes care of automatically 
replacing a bad disk in the stripe set thus keeping the "reduced performance 
duration", that  to a minimal.
 
- With lot of cache, fiber backplane and parallel writes to stripes, the "four 
I/O operations per read/write"  issue is mitigated.

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