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

Gah. This morning half-awake I realized the same thing. I'm lumping raid 
groups with aggregates/tiers in my muddled head and should (have) just 
created new raid groups in the existing two main tiers. Wish we'd had 
this conversation before I created two new tiers and moved a bunch of 
constituent volumes.

I'll get to work:

* moving the CVs back to the old tiers before they grow too much.

* destroy the two new tiers

* use the freed disks to expand the existing tiers.

On 8/27/2021 1:35 PM, Sebastian Goetze wrote:
> Why create a new tier (aggregate)? Why not expand both existing local 
> tiers with a RAID group of 12 (10+2)?
>
> Then, when you add another shelf, you'll just expand the RAID groups 
> from 10+2 to 22+2, expanding the local tiers again. (They can be up to 
> 800TB in size)
>
> Performance-wise with SSDs, the effect of a small RG-size is 
> negligible (well, you shouldn't go down to 1+2 or even 3+2. But 10+2, 
> you probably don't notice a thing, especially considering, that we're 
> talking about a relatively small controller here.
>
> IMHO the management advantages of having fewer aggregates/tiers would 
> be the deciding factor here.
>
> There's reasons for more local tiers, e.g. SnapLock, but I guess these 
> do not come into play here.
>
>
> Regarding your mention of "I could add half of them to each existing 
> tier/disk group and exceed the best practice by eight SSDs.": No you 
> can't.
> 26+2 is the maximum to which you can go per RAID group (technically 
> you could also do 26+3). So keeping RGs balanced would be the goal here:
>
> aggrx = (22+2) + (10+2)
>
> for both nodes. Then you can expand with another shelf to (22+2) + 
> (22+2) per node and will be perfectly balanced regarding RGs and Local 
> Tiers...
>
>
> My 2c
>
>
> Sebastian
>
>
> On 27.08.2021 19:34, Rue, Randy wrote:
>> Hi All,
>>
>> I've cabled up the second external shelf for our AFF-A220 and it sees 
>> the disks. Now I'm at a fork in the road.
>>
>> We currently have two local data tiers made up of 24 disks each, one 
>> on each node.
>>
>> Best practices at 
>> https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-psmg%2FGUID-EE30CDA9-095F-4DD1-9A29-BB9F0E55DB4F.html 
>> say a disk group of SSDs should be from 20-28 SSDs each.
>>
>> If I go to create a new local tier the default is to create two new 
>> tiers, one on each node. That would give me two disks groups of 12, 
>> below the best practice. How badly would performance suffer? Any 
>> other caveats? Reliability?
>>
>> I could put them all on one disk group, and on one node? Bleah.
>>
>> I could add half of them to each existing tier/disk group and exceed 
>> the best practice by eight SSDs. I believe I've seen discussions (get 
>> it?) claiming that top limit is flexible with SSDs, was it here? But 
>> when I add another shelf I'll have the same problem.
>>
>>
>> Seems like the clearest path forward for consistency and future 
>> expansions is to add two tiers with small disk groups. So, can anyone 
>> guess if I'll have a significant performance impact? Any other caveats?
>>
>>
>> Grateful for any guidance,
>>
>> Randy in Seattle
>>
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