A full save saves all files specified in the FILES statement completely, regardless of whether or not they have been changed since the last save.
An incremental save does not save all files indiscriminately. ARCHIVE first checks each file to be saved to determine whether it is new or has been changed since the last save. If ARCHIVE detects that the current contents of a file were already saved during the last save, the file is not saved again. Instead it is registered in the directory as “cataloged but not saved” (CNS).
Incremental saves can result in a considerable reduction of the time and storage space required for system backup carried out by the system support. For this reason, ARCHIVE executes system backup as an incremental save by default.
Full saves and incremental saves can be carried out on different volumes (e.g. full save to magnetic tape and incremental save to private disk).
Up to 255 incremental saves can be performed between any two full saves. After 255 incremental saves, ARCHIVE automatically executes a full save even if otherwise specified in the corresponding statement.
The type of save is controlled via the CHANGED operand of the SAVE statement. Specifying CHANGED=YES results in an incremental save, while CHANGED=NO causes a full save to be executed.
The scope of an incremental save can be further reduced by a partial save. Just as in an incremental save, the files which have remained totally unchanged since the last save are not saved. Those files that have been changed are checked by ARCHIVE to determine the parts (2-K blocks) that have been modified since the last full (not partial) save. Only these are saved in this run.
This means that both the most recent partial save and the most recent full save are required in order to restore a partially saved file.
A partial save partially saves either all files with LARGE in their catalog entry (CHANGED=YES,LARGE) or files of a specific size irrespective of the catalog entry (CHANGED=YES,integer).
Partial save is not possible for PAM files without a PAM key (BLOCK-CONTROL-INFO=NO), except in the case of PLAM libraries.
Incremental Save and Retention Period Update
Rare cases may occur, when a file is saved full within an incremental save, although the same file version exists in an older full save. In this case, the update of retention period and expiration date for the old full save is suppressed, see the section "Retention period and expiration date".
We recommend that you do not use the optional reps any more for suppression of the retention period and expiration date update (ARCHIVE and HSMS operation)