I have a configuration as follows – I want to maximise capacity without sacrificing performance:
1 x 2040HA – 12 x 300GB 15k
1 x DS4342 – 24 x 300GB 15k
I was thinking of splitting the disks 50/50 and having 18 per controller; however, I do not want to have 2 spares per controller – Can I increase RG0 to 17 disks (15 D + 2 P) or is it a bad idea to deviate from the recommended for just 1 disk? – Also, what about 12 for one controller and 24 for the other, increasing the RG on controller 2 to 23 (1 S, 2 P, 20 D)???
Bigger RG size yields more usable capacity, but means longer rebuild times in a case of a disk failure.
This leads us back to the 1 vs. 2 hot-spares dilemma:
- 1 hot-spare means (obviously) more capacity
- 2 hot-spares are required to enable Maintenance Center:
"If Data ONTAP drive health monitoring determines that a drive has surpassed an error threshold, rapid RAID recovery is initiated to a hot spare. [...] Maintenance Center requires that at least two hot spares are present in the system. NetApp recommends using Maintenance Center to provide additional intelligence for drive error discovery and correction."