The OPC (One Point Copy) function of ETERNUS Disk storage system is used to copy data from a transaction volume to an unused backup volume.
To perform a snapshot fast backup, take the following steps:
When the swstbackup command is executed ((1) in the following figure), an unused backup volume with the same size as the relevant transaction volume is selected from the unused backup volume management area.
If the number of backup volumes exceeds the number of preservation generations by performing backup, the history of the oldest backup volume is deleted, and then the volume is selected as an unused backup volume.
Data on the transaction volume is copied to the selected unused backup volume. The logical copy is instantly performed and the physical copy is started on the hardware ((2) to (4) in the following figure).
Backup carrier information is set.
Figure 3.2 Snapshot Fast Backup Processing
The snapshot fast backup is completed as soon as you confirm the execution of the backup. The actual data copying is performed internally by the OPC function of ETERNUS Disk storage system.
The QuickOPC function of the snapshot high-speed backup creates a snapshot image by only copying the data updated since the start of previous backup. This reduces the time for physical copying significantly.
For information on the QuickOPC function, refer to "Chapter 5 Backup Operation Using QuickOPC Function".
Note
If all the generations of backup volumes are being managed, and if no backup volume can be obtained from the unused region in the backup volume management area, backup copies cannot be created.
When the transaction volume is a volume group, copy processing by the OPC functions of ETERNUS Disk storage system is performed for the entire physical disk comprising the volume group. Therefore, when two or more logical volumes exist in a volume group, the data contained in all logical volumes is backed up (refer to the following figure).
Note
When using a volume group for backup operation, care needs to be taken with the following points:
When the transaction source volume is a volume group, construct a logical disk whose size matches that of the transaction volume, in a volume group different from the transaction group, and register this volume group whose physical disk size is the same as the transaction volume as the backup volume.
A "Describing Device Map File" is created to describe the pairing of matching transaction and backup volumes. For details, refer to "3.4.9 Preparing Device Map File". A "Device map" is mandatory if you are backing up using a volume group unit.
In backup processing, since the LVM configuration information on the backup volume is rewritten for the LVM information on the transaction volume, LVM configuration information is restored in the processing after backup. For more information on this, refer to "9.1.4 Notes on Restoration".
When backing up a volume group using an account with Administrator authority for backup, modify the scripts used for backup pre-processing and post-processing to unmount/mount all logical volumes in the volume group. For more information, refer to "Appendix A Pre-processing and Post-processing of Backup and Restoration".
When two or more physical disks exist in the volume group which is registered with a transaction volume, the backup operation results in an error.
Figure 3.3 Transaction Volume and Backup Volume for Two or More Logical Disks
