usermapper service query.

Hello 

I had a query on the usermapper.

as per the document of usermapper manual.

Every user of the EMC VNX, either a Microsoft Windows user or a UNIX/Linux user, must be identified by a unique numeric user identifier (UID) and group identifier (GID). As you probably know, it’s a little bit different with Windows. Windows does not use numeric IDs to identify users. Instead, it uses strings called security identifiers (SIDs). Therefore, before you configure the Windows file-sharing service (CIFS server), you must select a method of mapping Windows SIDs to UIDs and GIDs. The method you use depends on whether you have a Windows-only or UNIX/Linux and Windows (multiprotocol) environment. 

Every VNX user must be assigned a unique numeric UID and GID to indicate the ownership
of directories and files. The VNX uses directory and file ownership to apply and enforce
access permissions and quota limits.

Note: For connections from Windows users, file access checking is performed by using SIDs only.
This is done to prevent errors due to UID mismatches and to reduce dependency on the Usermapper
database.

----- END

my query is.
assume if only Windows environment, where in the access & permissions is controlled more by SID ( from the Windows AD ), UID/GID is not being used for user access / permissions. From that context what is the role of UID to SID mapping. 

in general if pure CIFS env, then why do we need mapping of UID to SID, why should we enable usermapper service.

one blog say it might be useful incase of setting up of quota other than that I'm not sure where else it will refer the mapping of SID to UID.

 

thank you
Yousuff K.