Re: options for adding a shelf/disks to an AFF-A220

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 <[email protected]> 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-psmg%2FGUID-EE30CDA9-095F-4DD1-9A29-BB9F0E55DB4F.html
> 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-status
>
> I'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