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Understanding Disk Array Availability

By touqeer9045 ·
Hi,

I'm new to this thus I'm trying to understand about calculating Disk Array Availability (DAA).

What I have understood so far is that availability is always 1, and Failure = 1÷MTBF.

Could someone explain in simple English how to calculate DAA.

Assuming I have 1TB and the time is 5 years, and the disk's MTBF is 1.6 millions hours (got this from Dell's website for a 15K RPM disk), I need to know the availability of this disk in 5 years, how do I calculate, what is the formula, I'm seeing , MTTl, MTTR, and MTTDL and getting confused.

Another confusion is, is disk array availability associated only with RAID.

Appreciate the assistance.

Currently I'm using this as reference : ecs.umass.edu/ece/koren/architecture/Raid/reliability.html

Also in the reference it says double disk failure, does the double disk mean any 2 disks or what, because once we find the availability of 1 disk would multiplying that into 2 NOT give us the double disk failure..

If anyone knows of any other good reference that explains in simple English.

Thank You

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