ONTAP Discussions

Expand aggregate & raid group


Hi Experts !


I need some info on what happens with ONTAP when you add more disks to an aggregate than the max allowed for the RAID group of that aggregate.


  1. What does ONTAP do in this case? Does it automatically create a new RAID group for the extra disks, or is there another way it handles it?
  2. Are there any performance or redundancy impacts on the aggregate after adding more disks than the RAID group's limit?
  3. Are there any best practices or recommendations to avoid issues in this kind of situation?
  4. If anyone's been through this, can you share your experience and how you managed it?

Here's my specific scenario: I have an aggregate with one RAID group (rg0) of 25 disks (RAID_TEC) + 2 spare, and the Max RAID Size is 29. What happens if I add 28 more disks to this aggregate ? This is to increase the capacity of a FlexGroup


Thanks experts !!



All from memory:

RAID size is including parity, in your case, depends on disk type etc I'd assume it will just suggest you to create a new raid group, or append the disks to fill your first RAID group, if you want to influence it, you can play with the maxraidsize value before and after...

Performance in RAID is negligible these days, even during re-construction, the main thing they worried about is availability of the aggr, the more disk in it the more likely you can hit double-disk-failure, and the more shelves it's spread on, the more likely you will have a disk shelf failure taking the aggr down (hence you see spare assignment and ADP being shelf oriented).

My go-to and take-away these days is:

1. let ADP do it's thing. as sometimes it's really hard to predict what logic they use for it.

2. use the GUI to see what it suggest doing with the new disks.

3. use the disk add command -simulate and see what it suggests.

4. play with maxraidsize to fit your vision.

5. Consider a new aggr, especially for different disk types/speed/end of life (of the disk, or the shelf).