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Backup: A Few Good Reasons

Novell Cool Solutions: Feature

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Posted: 9 Sep 2004

Having reliable data backups is essential, but sometimes the message can get lost. For example, a Novell user wrote the following:

"I recently had a friend suggest that backing up the NDS tree and objects was not really needed since we had Read/Write replicas of our tree on several servers in different locations. Should I be concerned about backing up the Tree/NDS objects? Help! Please explain!"

Sysop Sayings

A few of the volunteer Novell Sysops weigh in here on the importance of backups as well as some timely tips and strategies.

You should have a backup for two reasons:

  • Disaster recovery
  • In case you delete an object accidentally

What if a disaster strikes and you have lost all your replicas? Or what to do if you've deleted an object by mistake and that deletion have synched out to all replicas before you realize your mistake? In both these scenarios you need some sort of NDS backup, to be able to recover.

It's true that you can restore single objects from Arcserve, instead of an entire tree. But you need to be aware of the consequences. Realize that each object has references to other objects. For example a user could be member of a group. The user object references the group object in group memberships. The group object also references the user back in the group's membership list.

If you by accident delete the user, the user would be de-referenced from the group. If you then restore the user only you will end up with a mismatch. The user will reference the group, but the group will not reference the user. This will need to be fixed manually. Or when you restore, you restore both the user and the group. Hence you can understand that this could be very cumbersome, because you may end up having to restore all objects.

There are useful tools such as groupfix that can check and fix some of these issues, but a lot of references may not be so easy to restore.

If only one server dies and you have other replicas, your tree is still "alive," and all is (relatively) well in DS-land.

But ... if something happens to corrupt an object and that corruption is replicated to all your replicas, then having a tape to spin comes in handy. If something happens to all the servers at the same time, ditto.

If you need - for whatever reason, such as legal, testing, etc. - to restore some objects in the tree as they existed a month ago, not having a tape makes this rather difficult.

And let's say someone "accidentally" deletes a large numer of objects in the tree right before lunch or at the end of the day. The deletes will all sync out to the other replicas. No backup = pain.

The main vehicle in DS for safety is redundance. I do "dsrepair -rc" on all my boxes for disaster recovery. I do tsands backups, but I hope I never have to restore an object.

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