/sys$common/syshlp/helplib.hlb MOUNT, Qualifiers, /DATA_CHECK  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /DATA_CHECK[=(keyword[,...])]

    Overrides the read-check or write-check option (or both)
    specified for a volume when it was initialized.

    The keyword, READ, performs checks following all read operations,
    and the keyword, WRITE, performs checks following all write
    operations.

    You can specify either or both of the keywords. If you specify
    more than one keyword, separate them by commas and enclose the
    list in parentheses.

    If you specify the /DATA_CHECK qualifier without specifying a
    keyword, MOUNT defaults to /DATA_CHECK=WRITE.

    Example

    The following command mounts a volume labeled SAM on CLEMENS$DKA2
    and assigns the logical name BOOK. The /DATA_CHECK=READ qualifier
    overrides a previous INITIALIZE/DATA_CHECK=WRITE specification,
    so that subsequent read operations on BOOK are subject to data-
    checking operations.

    $ MOUNT/DATA_CHECK=READ CLEMENS$DKA2: SAM  BOOK