An existing allocation might not match your request even though
it is associated with the same ddname you specify. Because the ddname
is going to be associated with the resource that is allocated to your
program, the system gives the existing allocation a new ddname, of
the form ‘SYS’ followed by five digits. The association of
a system-generated ddname with an existing allocation cannot occur
when the existing allocation:
- Is in use
- Is open
- Does not have the convertible attribute
- Is associated with a permanently concatenated group that does
not represent an entire generation data set group or a multi-device-type
VSAM data set.