IBM DS3400 Configuration Question - Hotspares

I am going to describe my environment first, and then at the end make a simple question:

I have a DS3400 SAN in place, there is the main controller with 12 x 450GB SAS drives in it.

When this unit was purchased, the individual setting it up had made two RAID 5 arrays and left the last drive for a hotspare.  All the data resides on 2.4TB of disk across these two arrays.

We have moved our servers to VMWare, and in doing so have added two more EXP3000 trays to this SAN with a addition of 24 x 450GB SAS disks.  The second and third tray are configured with 22 drives in a RAID 10 array with enclosure loss protection.  The last drive in each tray is reserved for hotspare.  Of the 4TB of usable array space, my VMFS only takes up 1.5TB so I have some free space to work with for now.

My intention is to move all the data temporarily to the new RAID10 array, delete the old RAID 5's and build a raid 10 array across the 12 x 450 disks, then move the data back to the new R10 array on tray 1.  Doing this will give me 2.7TB of usable disk on a much better RAID array.

So, after that long story, here is my question:

If I use all 12 drives from Tray 1 and make a RAID 10 array, if I have a drive failure, will one of the hotspares from tray 2 or 3 actually take over for the failed drive on tray 1?  Or do I need to establish a pair of hotspares on tray 1 as well and only use 10 disks for the array?

Thanks
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TheMetalicOneAsked:
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RaducanuCommented:
Hello,

you do not need one hotspare per enclosure. You just can configure one hotspare for your DS.
 IBM Redbook wrotes:
There is no definitive rule as to how many hot spares you have to install, but it is common
practice to use a ratio of one hot spare for about 30 drives of the same type.


Also please check this:

Best practice: When assigning disks as hot spares, make sure that they have enough
storage capacity. If the failed disk drive is larger than the hot spare, reconstruction is not
possible. Ensure that you have at least one of each size or all larger drives configured as
hot spares.
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TheMetalicOneAuthor Commented:
Perfect, thanks
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