[Samba] Sudden unexplained slowness on share (caused by duplicate UID?) SOLVED - nogroup 65534

[ash-samba at comtek.co.uk]

On 31/08/16 17:49, ash-samba--- via samba wrote:
> Hi,
>
> We have 5 Samba domain controllers, and 4 file servers. All are 
> 4.2.10-Debian. Our file servers have been working fine until recently 
> (on the 26th), when suddenly access to the 
> \\users.store.example.com\user share (hostname p-cats) became 
> extremely slow.
>
> Access to other shares on other machines is fine, and users is 128G 
> total (smaller than other shares). The machine isn't under 
> CPU/memory/IO/network strain, and accessing the file share via 
> SCP/shell is fine. Most clients are Windows 7, and are using offline 
> files.
> [...]

Just to provide closure for future googlers:

It appears that this problem was due to some files/folders which had the 
group "nogroup" set. Any attempts to list such files or folders caused a 
delay to all active connections.

The unix group nogroup on Debian has the UID 65534, and did not exist 
within AD. We use the configuration:

         idmap config * : backend = tdb
         idmap config * : range = 1000000-1999999
         idmap config EXAMPLE : backend  = ad
         idmap config EXAMPLE : range = 1000-999997

We also discovered some files had somehow acquired posix ACLs which 
included nogroup, we had to delete the ACLs too (our server was supposed 
to be using unix UID/GID permissions only - no idea how Samba could have 
added ACLs!)

Ash