Understanding Disk Array Availability..

Question

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 : http://www.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

DELL-Sam L · Answer

Hello huud,

Here is the link to Dell EMC Unity technical documents and videos. https://www.dell.com/support/article/us/en/04/sln310140/dell-emc-unity-technical-documents-and-videos?lang=en

Here is the link to understanding Dynamic Pools https://www.emc.com/collateral/white-papers/h16289-dell-emc-unity-dynamic-pools.pdf

Here is also a link to understanding how Unisphere works. https://www.emc.com/collateral/white-papers/h15085-dell-emc-unity-unisphere-overview.pdf

Here is also the link to the best practice guide as well for a unity system. https://www.emc.com/collateral/white-papers/h15093-dell-emc-unity-best-practices-guide.pdf

Here is the link to introduction to the unity platform. https://www.emc.com/collateral/white-papers/h15084-dell-emc-unity-introduction-to-the-platform.pdf

If you have a drive fail and your system is still under warranty, then we will replace the drive with the same size & speed as the failed drive. If that drive size is not available, then we will send you the next available larger size drive.

A double disk failure is when you have 2 drives that fail on the same lun. If you have two drives fail on two different luns that is seen as a single drive fail on the lun.

Please let us know if you have any other questions.

Unity

Understanding Disk Array Availability..

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