BS2000 offers an integrated solution for saving a pubset to so-called snap units of an external storage system during ongoing operation. This function is offered under the name Snapset. It is available for the storage systems ETERNUS DX/AF from Fujitsu.
BS2000 also supports data backup by replication functions of external storage systems. For details, see the “SHC-OSD” manual [48].
Principle of the Snapsets
A Snapset is the directly available backup of a pubset to so-called snap units of a storage system. A Snapset is used to restore lost data (e.g. after inadvertent deletion). The complete pubset can also be restored to the status at the time the Snapset was created. Both SM and SF pubsets can be backed up. Snapsets are generated by systems support or the HSMS administrator during ongoing pubset operation and deleted again later as required. Up to 52 Snapsets can exist for a pubset (provided this maximum number is supported by the storage system).
Within the storage system, snap units use a block-by-block incremental procedure, and only require storage space of their own for blocks which differ from the original.
This means that saving to disk using the snap technique also makes economic sense: When, for example, 10 backups are created in one day from a pubset with a capacity of 100 GB, if cloning were used 1 TB of additional disk storage space would be required. However, when Snapsets are used, the amount of additional disk storage space required depends on the volume of changes on the pubset. If the volume of changes per day is 20%, in the example above additional disk storage space of only 0.2 TB (20% * 10 backups * 100 GB) would be required.
Snapsets are available exclusively for restore purposes (i.e. read-only access): They are placed in service automatically when they are generated. Existing Snapsets are generally placed in service when the associated pubset is imported.
Users can access Snapsets using the following functions:
Display information on existing Snapsets (i.e. pubset backups)
Display information on restorable files and job variables
Restore files and job variables
Restore pubset (privileged users only)
The following software products also enable Snapsets to be accessed:
LMS enables members of PLAM libraries to be selected and copied to Snapsets (see the “LMS” manual [29]).
HSMS enables files and job variables to be transferred from a Snapset and to a backup archive (see "Saving a Snapset to a backup archive" in section "Restoration of files and job variables" and the “HSMS” manual [24]).
The Snapset functions are available in shared pubset mode on all the systems involved. The requirements for this (BS2000 versions of the pubset sharers and of SHC-OSD) are described in the current BS2000 Release Notices.
In BS2000 you can use up to 52 Snapsets. In addition, program interfaces which in functional terms correspond to the command interfaces mentioned above are offered for accessing the Snapsets (see the “DMS Macros” manual [20]).
VM2000 supports the use of Snapsets by the guest systems (see the “VM2000” manual [60]).
Application area of Snapsets
Snapsets are used on a short-term basis as a backup when the files or job variables of a pubset are lost. An entire pubset can also be restored quickly to a particular status with the RESTORE-PUBSET-FROM-SNAPSET command. They are not suitable for long-term backups or data transfer. The snap units used by Snapsets are normally local copies within a storage system and thus offer no protection when the storage systems fail. You are therefore urgently recommended also to back up Snapsets with (see "Saving a Snapset to a backup archive" in section "Restoration of files and job variables").
Private disks (or files on private disks) cannot be saved on Snapsets.
The operation of Snapsets can be combined with the simultaneous use of disk copies on the basis of local mirrors in the same pubset provided this is possible in the storage system concerned.
Mixed mode of Snapsets (/CREATE-SNAPSET) and Snapshots (/START-SNAP-SESSION, /ACTIVATE-SNAP) is not supported .
These other usage modes are described in the “HSMS” [24] and “SHC-OSD” [48] manuals.
Restrictions:
The pubset cannot be restored from a Snapset if a clone session is still active for this pubset.
Overview of the interfaces for working with Snapsets
All the commands for Snapset mode, saving to Snapsets and restoring from Snapsets are offered in the SDF application area “SNAPSET”. These commands are described in the “Commands” manual [27].
Comman | Function |
ADAPT-SNAPSET-ACCESS 1 | Adapt access to Snapsets in the case of remote replication |
CHECK-SNAPSET-CONFIGURATION 2 | Check the Snapset configuration and activate available Snapsets |
CREATE-SNAPSET 2 | Create a Snapset |
DELETE-SNAPSET 2 | Delete a Snapset |
LIST-FILE-FROM-SNAPSET 3 | Provide information about files on a Snapset |
LIST-JV-FROM-SNAPSET 3 | Provide information about job variables on a Snapset |
RESTORE-FILE-FROM-SNAPSET 3 | Restore files on the basis of a Snapset |
RESTORE-JV-FROM-SNAPSET 3 | Restore job variables on the basis of a Snapset |
RESTORE-PUBSET-FROM-SNAPSET 2 | Restore a complete pubset on the basis of a Snapset |
SET-PUBSET-ATTRIBUTES 2 | Determine the maximum permitted number of Snapsets for the pubset (SNAPSET-LIMIT operand) |
SET-SNAPSET-PARAMETER 2 | Define the Snapset environment |
SHOW-PUBSET-ATTRIBUTES | Display information about, among other things, the Snapset limit |
SHOW-SNAPSET-CONFIGURATION | Display information about existing Snapsets and the Snapset configuration |
2 Privilege TSOS or HSMS-ADMINISTRATION required
3 There is also a program interface for these commands, see the “DMS Macros” manual [20].