Two of you just reminded me what I should have figured out earlier, see my other response.
Thanks!
On 8/27/2021 1:38 PM, John Stoffel wrote:
"Randy" == Randy Rue randyrue@gmail.com writes:
Randy> Hi All, Randy> I've cabled up the second external shelf for our AFF-A220 and it sees Randy> the disks. Now I'm at a fork in the road.
Randy> We currently have two local data tiers made up of 24 disks each, one on Randy> each node.
Randy> Best practices at Randy> https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-psm... Randy> say a disk group of SSDs should be from 20-28 SSDs each.
Don't you mean 'Raid Group' here? In any case, I'd just split the disks in half and add them to the aggregates on each head, to create some new RGs.
But it would help if you could show your current setup with:
storage aggregate show-statusI've got an a200 running 9.3.P10 (yes, I know it's old... sue me.) and we haven't had any issues, but I admit we haven't grown it either.
Randy> If I go to create a new local tier the default is to create two new Randy> tiers, one on each node. That would give me two disks groups of 12, Randy> below the best practice. How badly would performance suffer? Any other Randy> caveats? Reliability?
I don't think you'll notice any performance problems, the issue really comes down to overhead you lose due to having to dedicate more disks to parity.
Randy> I could put them all on one disk group, and on one node? Bleah.
Randy> I could add half of them to each existing tier/disk group and Randy> exceed the best practice by eight SSDs. I believe I've seen Randy> discussions (get it?) claiming that top limit is flexible with Randy> SSDs, was it here? But when I add another shelf I'll have the Randy> same problem.
Once you add another shelf after this shelf, you'll end up balancing things since you'll ideally fill your raidgroups to a larger number of data disks.
Randy> Seems like the clearest path forward for consistency and future Randy> expansions is to add two tiers with small disk groups. So, can Randy> anyone guess if I'll have a significant performance impact? Any Randy> other caveats?
I don't think you'll notice any problems, if only because the A220 isn't the highest performing system anyway. If you've got the time, setup a new aggregate on one head with the same setup as currently, then partly fill it and run some performance tests.
Good luck, John