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I will start with my question and then make a short example:

Is it a good idea to split a disk into multiple partitions and create different disk Arrays (raid1/raid5) with those paritions? Are there any Problems/risks?

And now the example:

Say I have three disks. Two have the same size and one has twice as much:

Disk a: |---------------|
Disk b: |---------------|
Disk c: |-----------------------------------|

Now I would create the following two disk Arrays

     Array 1           Array 2
|-----Disk a----| |-----Disk b----|
|----Disk c/1---| |----Disk c/2---|

Disk c was split up into two partitions, one Partition is used to create a raid1 with disk a and the other Partition is used to create a raid1 with disk b.

With this Approach, all the disk space is used and nothing is wasted. I know that a failure of disk c will degrade both disk Arrays. Are there any other Problems/risks involved?

Thomas Sparber
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2 Answers2

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Is it a good idea

No, and we try very hard to avoid R5 these days too by the way, please don't - stick to R6/60 and 1/10.

Chopper3
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  • Thank you very much for your answer. Can you please explain in more Detail why it is not a good idea **to use one disk in two arrays**? – Thomas Sparber Feb 15 '16 at 10:27
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    It'll affect your performance as one disk will be busy with two disks when it comes to writes - this will be especially painful if you're using 'spinning' disks as the heads will inherently be in wildly different parts of the disk and so will be hopping back and forth all the time. If you're doing nothing but reads it's still not a good idea, otherwise other people would be doing it right, and they're not. – Chopper3 Feb 15 '16 at 11:27
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The only risk is what you've already identified. This is a common practice on smaller Netapp systems, however the tradeoff is a much increased level of overhead.

edit: to clarify, on Netapp, all disks are divided into the same partitions, and raids are made from those. All the same raid level, all the same disks. In your scenario, as @Chopper3 mentioned, you'll have uneven amounts of work being done on different disks, which is bad.

Basil
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