can i mix RAID-DP and RAID-TEC in the same aggregate?

[frank glacier]

I have a customer wanting to mix 8TB and 4TB drives using 2 raid groups in the same aggregate on in a FAS2750... can they make the 4TB raid-dp and the 8tb RAID-TEC?

[sweet hamlet]

nope, that doesn't work, the whole aggregate needs the same redundancy

[neon spire]

and the same drive size, obviously

[sweet hamlet]

different RAID groups can have different drive sizes within the same aggregate

[neon spire]

oh okay, I was not aware of that...

[pulsar lake]

I can't think of any reason why you can't have different RAID protection in RAID groups comprising an aggregate. What you can't mix is drive performance/technology, unless it's explicitly a hybrid aggregate (SSD tier, HDD tier).

[sweet hamlet]

well, it does not work. And IMHO it does not make sense either -- if you want to have some data with less protection than other data, you have to put it on separate aggregates. Those can then have different RAID levels of course. But since all data in an aggregate is mixed you would have no control over what data gets what protection

it's the same argument as with mixing SATA/SAS/SSD: if you have some data with faster requirements and some without, you need to separate them on different aggregates. Otherwise you would have no control over what data is "fast" and what is "slow", since all data is "spread" across the whole aggregate

fun fact: using diag commands you actually can mix drives of different speed characteristics in an aggregate, while mixing different RAID protection levels is still not possible 😉

[pulsar lake]

Hmm... I'm going to have to look into that. If possible, DM over the error output you see when you try it. Thanks!

I guess the one exception to this is a hybrid aggregate - SSD tier can be different protection than the HDD tier.

[sweet hamlet]

The exact error is Error: command failed: Cannot specify raidtype in this operation on a non-Flash Pool aggregate.

this has never worked in ONTAP. Even for FlashPool it was not possible at first, they had to implement this when people kept complaining that they had to lose 2 of those expensive 100GB SSDs for parity just because their aggregate had raid_dp 😉

then again, something I have always wondered is whether it will work if you manually build the raidtree in diag-mode with different raid levels and then put an aggregate on that... 🤔 maybe I'll try that in the simulator. It might work. Even RAID-0 aggregates work if you build them manually, so... 😉

[pulsar lake]

Yeah... looking at the man page:
https://docs.netapp.com/us-en/ontap-cli-9141//storage-aggregate-modify.html#description
The raid-type modify granularity is by disk-type. In the OP's example, if both capacities are FSAS, you're stuck.

[sweet hamlet]

no, it is per aggregate (unless FlashPool aggr)

[sweet hamlet]

the note about the disktype is not very helpful. It also applies to FP only. One could read it as different types of SATA disks could have different RAID levels (e.g. BSAS and ATA) but that's not possible