VA7100 Available Space

[Amiel Tutolo]

I have a VA7100 currently installed with 10 36GB drives. I am wanting to add 73GB drives, I know this can be done. Our reseller says I have to add 4 of these to the array but we won't get much space due to overhead. Here are my questions:
1) Do I have to add 4 73GB drives?
2) How much space do I gain? I figure 263GB.
I based this on losing only 1 73GB drive and not a 36GB drive for hot spare. Is this true as well.
3) If I have to add 4 73GB drives then from a cost/gb am I better off adding 4 more 36GB drives, which are about $600/drive cheaper?

Just some thoughts I am having. Any help is greatly appreciated.

[Peter Mattei · Accepted solution]

You VA7100 with 10x 36GB disks, set to AutoRaid and sparing to 1 should give you app. 215GB max usable capacity.

If you would add 5x 36GB disks you would reach 367GB max usable capacity.

Adding 5x 72GB disks would give you around 460GB max usable capacity.

Reasons:
A 36GB disk will give you round 33GB net.
A 72GB disk will give you round 66GB net.

If you would add just one 72GB disk you will only gain 33GB. Only half of the disk can be used.
Adding the second 72GB disk gives you another 33GB. Now both 72GB disks will be fully used, but you will have to reserve 66GB spare space.
By adding the third 72GB disk you will finally start gaining 66GB per disk.

Cheers
Peter