You can apply Access Control Lists (ACLs) on qtrees by using NTFS or mixed security styles, but not by using the UNIX security style. Therefore, changing the security style of a qtree might affect how quotas are calculated. You should always reinitialize quotas after you change the security style of a qtree.
If you change the security style of a qtree from NTFS or mixed to UNIX, any ACLs on files in that qtree are ignored and the file usage is charged against the UNIX user IDs.
The following example shows how a change in the security style of a qtree results in a different user being charged for the usage of a file in the particular qtree.
Suppose NTFS security is in effect on qtree A, and an ACL gives Windows user corp\joe ownership of a 5 MB file. User corp\joe is charged with 5 MB of disk space usage for qtree A.
Now you change the security style of qtree A from NTFS to UNIX. After quotas are reinitialized, Windows user corp\joe is no longer charged for this file; instead, the UNIX user corresponding to the UID of the file is charged for the file. The UID could be a UNIX user mapped to corp\joe or the root user.