Best practice is a minimum of one hot spare per 30 drives.

The section 'Hot Sparing' in the EMC CLARiiON Best Practices for Performance and Availability, FLARE Revision 28.5 (available on Powerlink) contains a longer discussion, and an example of a hot sparing layout.

Typically on a general practice, we keep at least 1 Hot spare for every 30 drives. However, you can have more Hot spares - it's a trade off you between reserving disks against having more protection for disk failure.

Also it may depend on how the array is supported - if you get any disk failure replaced very quickly, that helps with lesser hot spare ratio.

However, at times when you need to follow a template - you may have to keep hot spare for every 15 drives - say for example, configuring disks for a NAS gateway - you may have to create 1 hot spare in each enclosure.

I am sure there will be more replies to this thread - I am happy to put my 2 cents
Have a great weekend,
Regards,
Sandip

There is also a good document on Powerlink titled "EMC CLARiiON Global Hot Spares and Proactive Hot Sparing". It is a must read in my opinion when planing your hot spares for your array.

Lots of good info in there!

i have a couple of DAEs with 1TB drives, because these drives are much slower than FC i am afraid of double drive failure during hot spare rebuild, so i go with 1 hot spare per DAE.

Rule of thumb 1 per 30 FC and 1 per 15 SATA, unless you go for RAID6.....

Idealy I'd have 1 HS on every bus and for each type an HS, so if you have 2 buses with 146GB15k and 400GB10k and 1TB7k2 on each bus, I'd go for (at least) a HS of each of the 3, depending on how many drives of each type is on each bus.

Hi,

Thank you all for your answers

Consty

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glen

With RAID6 you can do with 1 HS per 30.

In the end it's YOU who decides.....