The EC function of ETERNUS Disk storage system is used to copy data from a transaction volume to an unused backup volume.
To perform synchronized high-speed backup, take the following steps:
When the swststartsync 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 and backup synchronous processing begins.
After the synchronous copy completes, the volumes enter equivalency maintain state which maintains the equivalency of the transaction volume and backup volume. ((3) in the following figure).
Note that the equivalency maintain state does not guarantee equivalency of the transaction volume and backup volume.
When the swstbackup command is executed ((4) in the following figure), the backup synchronization processing stops and the backup history information is registered.
When the generation number of the newly backed up data exceeds the number of generations of backup history being kept, the oldest backup volume is treated as an unused backup volume.
Note
The swstbackup command cannot be executed before the transaction and backup volumes have become equivalency maintain state.
Figure 3.4 Backup Using Synchronized High-speed Backup Function
During synchronous high-speed backup using the Suspend/Resume function, the equivalency maintenance status of EC can be set to Suspend or Resume. The synchronous backup process is therefore faster because the function can create a differential copy from the Suspend state.
For information on the Suspend/Resume function, refer to "Chapter 4 Backup Operation Using Suspend/Resume Function".
Note
If all 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 EC function of ETERNUS Disk storage system is performed to 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.
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.
