The EC(Equivalent Copy)/REC(Remote Equivalent Copy) function of ETERNUS disk storage systems is used to copy data from a transaction volume to an unused backup volume.
To perform synchronized high-speed backup, take the following steps:
Execute swststartsync (Backup synchronous processing start command) ((1) in the following figure), the transaction volume and an unused backup volume with the same capacity are selected from the unused backup volume management area and synchronized backup processing is started.
The transaction and backup volumes reach an equivalent state. From this point on, equivalence between the transaction volume and backup volume is maintained. This status is referred to as equivalency maintenance status ((3) in the following figure).
Execute swstbackup (Backup execution command) ((4) in the figure below). The backup synchronization processing stops and the backup history information is set.
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
swstbackup (Backup execution command) cannot be executed before the transaction and backup volumes have become equivalent.
Figure 4.4 Backup using the 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, see Chapter 5 Backup Process That Uses the 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 and REC functions of ETERNUS disk storage systems is performed to the physical entire 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 "4.4.10.1 Describing a device map file" is created to describe the pairing of matching transaction and backup volumes. For details, refer to "4.4.10 Preparing a 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 will be rewritten for the LVM information on the transaction volume, LVM configuration information is restored in the processing after backup. For more information, see "Appendix A Pre-processing and Post-processing of Backup and 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, see "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 will results in an error.
In the case where the backup volume is a volume group, do not execute the vgchange (1M) command while executing synchronous processing (EC/REC). If the backup volume becomes deactivated during the execution of synchronous processing, it will not be possible to reactivate it. In addition, it will not be possible to stop synchronous processing, the backup execution command, the backup synchronous processing cancel command, etc. If accidentally deactivated, use ETERNUS Web GUI or similar, to forcibly stop synchronous processing, and then activate the backup volume.
