Knowledgebase: Using disk drives
Backup to disk using Synchronize
Posted by Sven Koester, Last modified by Sven Koester on 01 October 2008 8:00
The PresSTORE Backup module allows to create backups on disk by simulating a media changer and "virtual" tapes. This allows to perform any backup job that can be done on physical tapes on hard disks. Files in the backup are saved in big disk and idex information is maintained which file is where in the backup.

The PresSTORE Synchronize module follows a different paradigma. With Synchronize, a one to one copy of all files is created on a destination drive. This includes all file attributes, so the destination drive holds an exact copy of the soruce. Like the Backup module, Synchronize can be restricted to specific directories, so one can create a snapshot of specific folders or of the whole volume.
This mechanism can be used in backup scenarios in multiple ways; this articles will take a closer look the these posibilities.

Using Synchronize for disk backup
The Synchronize module has two features that allow creating a complete backup with multiple copies, cycles and versions:
  • The cycles allow to save multiple snapshots of the source in different stages: When Synchronize cycles are set in the Synchronize plan window, PresSTORE will maintain a directory __CYCLES on the destination and will keep the complete set of data there each time a full synchronize will create a new snapshop. This feature is comparable to the backup cycles configured in backup plans. The number of such cycles that shall be kept is configurable.
  • The versions feature allows an even finer granulation. After creating a snapshot on the destination drive, Synchronize can keep the destination up to date by performing incremental updates in short regular intervals, e.g. every 30 minutes. Doing so while a file is edited on the source, the destination file will be updated and the old version would normally be lost. With the versions enabled, Synchronize will keep these previous versions of each file in a separate directory __VERSIONS.
Using cycles and versions, the Synchronize module used for backup has multiple advantages:
  • Files are directly accessible without management overhead
  • Previous versions can be kept to be able to go back a few hours in the working process
  • Cycles allow to save the state of one or two weeks ago, just like a grandfather-fahter-sun backup would do.

Achieving larger time windows for tape backups

In a more complex environment, situations may arise where the time window for a backup becomes very small. Namely in an environment where multiple clients shall be saved in a backup, Synchronize may be used to maintain a copy of the client's data. This way the backup can be done overnight from the synchronized drive while the clients are switched off, unavailable or again busy in a production.

Spreading network load over time

In case a backup is required for data that must be transferred over slow lines, e.g. via VPN from another office, it is often not possible to get the complete data in an adequate speed.
Here, an initial copy of the data can be done with synchronice in the foreign office, and the data can be kept up to date by doing an incremental synchronization. This way the incremental save in shorter intervals allows to spread the required network traffic over a long time and the backup of the data onto tapes can be done from the local
synchronized disk.
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