Question: I'm trying to figure out continuous "Unable to write SPDistributedCache call usage entry." error in ULS and some instructions like [this](http://www.sharepointfire.com/2013/11/the-specified-user-or-domain-group-was-not-found/) suggests that issue might be with super accounts having incorrect username.

The user accounts used for superreader and superuser accounts are currently set in domain\superuser and domain\superreader format to web app's portalsuperreaderaccount and portalsuperuseraccount properties.

But I'm wondering if they would need to be updated into i:0#.w|domain\username format instead to fix issues?

As far as I know these both formats should resolve fine but thinking if this still could be an issue.

Answer: 
I tried contacting Microsoft for the same requirement but I found this question is already answered by Microsoft support team.

The reply from Microsoft Team was like

> 
> Currently, the sub site limit is 2,000 for Office 365 subscriptions.
>  We can see the limit here: [SharePoint Online software boundaries and
>  limits](https://support.office.com/en-us/article/SharePoint-Online-software-boundaries-and-limits-8f34ff47-b749-408b-abc0-b605e1f6d498?ui=en-US&rs=en-US&ad=US). For any changes, we will update the News in our [Office
>  365 roadmap](http://fasttrack.microsoft.com/roadmap).
> 
> 
> 

You can find this thread [here](http://answers.microsoft.com/en-us/msoffice/forum/msoffice_o365admin-mso_dep365/actual-sub-site-limit-per-site-collection/92bce614-6bc7-480f-828c-807ea850fc6f).

Now the actual point. The [article](http://www.metalogix.com/Blog/Blog-Article/metalogix-software-blog/2014/09/17/sharepoint-online-ups-site-collection-sub-sites-storage-and-file-sizes-beyond-sharepoint-on-premises) which says that the sub site limit is 100,000 is written on **Sep 17,2014** and they say that Microsoft has increased the limit in last 6 month while the Microsoft says its still 2000 on **November 20,2015**. 

So we can't say anything until we personally don't try. The procedure used in [this](http://geekswithblogs.net/ThorvaldBoe/archive/2015/12/18/finding-the-maximum-number-of-sub-sites-in-sharepoint-online.aspx) can be used to try and find actual limit. The variation may be due to subscription plan or available storage.
I think 2000 subsite per site collection is just a threshold value.

There will be impact on performance if your subsite count is more than 2000.

Thats why Microsoft recommends upto 2000 subsites per site collection.

<https://support.office.com/en-us/article/SharePoint-Online-software-boundaries-and-limits-8f34ff47-b749-408b-abc0-b605e1f6d498>