Yeah, something I have seen and not like also. I think this was added in 9.6 or 9.7 and still exists up to at least 9.9.1 and likely beyond. Here is something to ponder....
Personally, I would do this:
1. Upgrade to ONTAP 9.9.1P10 or 9.10.1P4
2. Use FlexGroups!
FlexGroups is a method to distribute NAS data over multiple controllers and multiple aggregates.
In your case, it sounds like you have 36 drives (12 internal + 24 external). You are limited to a MAX of 29 drives in a RAID-TEC aggregate. Remember, the larger the RAID group, the longer (much longer) it takes to rebuild a drive. I tend to stay closer to 20 using RAID-TEC. I would end up with something like this as a base:
12 Partitioned drives using Root-Data partitioning. 24 Whole disks (no partitions yet)
6 Root partitions on Node 1 and 6 root partitions on Node 2
I am not a fan of the gui when making aggregates. Although more recently it has become better, I still use the CLI for nearly everything (more control).
- Note which disks are partitioned
- storage aggregate show-spare-disk
- Create an aggregate on each node starting with the six partitioned disks plus one WHOLE disk. ONTAP will auto-partition a drive to be added to the aggregate as needed. A new raid-group will use whole drives. Anything in the partitioned raid-group will be partitioned!
- aggr create xxx01 -node node-0x -disklist 1.0.0, 1.0.2, 1.0.4, 1.0.6, 1.0.8, 1.0.10, 1.1.0 -raid-type raid_tec -maxraidsize 16
- aggr create xxx02 -node node-0x -disklist 1.0.1, 1.0.3, 1.0.5, 1.0.7, 1.0.9, 1.0.11, 1.1.1 -raid-type raid_tec -maxraidsize 16
- Add disks to each aggregate. Like before, since the RAID-Group is using partitioned drives, any drives added to the RAID-group will be partitioned also
- aggr add-disks -aggr xxx01 -diskcount 9
- aggr add-disks -aggr xxx02 -diskcount 9
- Now you have two aggregates, same size, one on each node. If using 36 drives, you should have 2 spares left on each node. If you have fewer, then ONTAP will complain regularly.
When using spinning drives, ONTAP wants you keep to keep 2 spares per controller. When using SSD/NVMe drives, ONTAP will let you use one.
Now....what about a failure: ONTAP will auto-partition any drive it needs to replace a failed drive!
Now create a flexgroup and let your data distribute across both nodes and aggregates and improve your NAS performance! Note: your Flexgroup should be at least 800GB in size. Minimum Flexgroup members are 100GB each. A normal flexgroup will have 4 members per aggregate.
Use the GUI or something like this:
vol create -volume myflexgroup -aggr-list xxx01,xxx02 -aggr-list-mult 4 -size 1T -juntion-path /myflexgroup -space-guarantee none
This will make an 8 member FlexGroup called myflexgroup with each member, thin provisioned at about 128G each mounted in the ONTAP namespace at /myflexgroup