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Disk Arrays
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Amount Of disk used for redundancy

Occasional Advisor

Amount Of disk used for redundancy

I don't understand
How the amount of disks used for redundancy is calculated ?
Is it possible to reduce this quantity ?

You can view the result of armdsp -a commande in the attached file.

Peter Mattei
Honored Contributor

Re: Amount Of disk used for redundancy

Well, you only have 5 disks in the array!

So here is the calculation:
1. Your VA7100 has set active hot spare to on, which is recommended! This will the array allow to still be redundant after a disk failure. So these are the first 16.687GB = 1 disk. .

2. The VA needs some space to store metadata and the virtualization. Some GB.

3. The VA7100 stores data either in RAID01 or RAID5DP (also known as RAID6) RAID5DP stores 2 parity blocks in order to increase availability in larger disk configurations.
In Raid01 you use two disks for mirroring to present one disks capacity. This will leave approximately the value of 2 disks for your use. 2x 16GB = 32GB (minus metadata)
In Raid5DP it will take 2 disks for parity information, so 4 disks minus 2 disks = 2 disks net.

To get more usable capacity you have to add more disks! The good thing is, that if you add one 18GB disk you will gain the full capacity of 16GB formatted capacity! (sparing and parity capacity is already reserved)

I love storage
Occasional Advisor

Re: Amount Of disk used for redundancy

Thank you Peter you confirmed to me what I thought. Both redundancy discs are not
taken by the RAID10 but well by RAID 5DP. When I add a new disc I
recover well the whole capacity of the added disc

Thank you