2011-03-29 05:37 AM
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)???
Just looking for some advice and ideas?
2011-03-30 12:00 AM
In your case 1 spare per controller is fine.
How to divide your disks is ultimately up to you. I.e. 12/24 if you need more performance/capacity on the other controller.
If you ever need to upgrade the 2040 to a 32xx system, you can't reuse the internal disks, in which case 12/24 is easier to migrate.
You can increase the size of the raidgroup to 17 (max is 28).
Do this before adding disks, or else ontap will try to create a 2nd raidgroup, in which case you will end up with uneven RG's.
2011-03-30 01:20 AM
Will increasing the RG by a mere one disk have any negative impact?
Also, if you buy a 2040HA both root vols will be located within the unit - If at a later date you buy a 4324 can you move the root vol of one controller to the tray so you can have a 12/24 split?
2011-03-30 01:32 AM
Here is a very informative thread about RG sizes:
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."