Regarding Online Backup

[Severus]

Hi,
I have a question regarding the online backup. Suppose I am taking an online backup of an open DB that started at 00:00 and end at 18:00. At 20:00 the system crashed. Now my question is after recovering from the backup what will be the time of the data that I'll get. Would it be 00:00 or 18:00?

[steven Burgess_2]

Hmmm

Are there any changes being made to data during the backup ?

Steve

[Rajeev Shukla]

That depends on what type of backup software you are using.
Some softwares take a snapshot at 00:00 and then backup(which is called online backup because you dont have to take the Database Offline)In which case you'll retreive the data till 00:00.
Some backups softwares make the DB Offline and then start the backup and bring the DB online after the backup is complete. In this case you can retreive the data till 18:00.
Also if you are backing up the Archive logs then you should not have problem in getting the Data Base up to the say 20:00 when your server crashed.

Rajeev

[Steven E. Protter]

I would be amazed if you got anything useful out of that backup.

It took far too long to get done.

Assuming you used an approved tool from the database vendor (rman in the case of oracle), you'll get something you can restore, but the recovery process will take as long as the backup.

If trasnactions are happening on this database they are supposed to be committed by the backup as it goes through its process. It is supposed to but new transactions on hold while it gets a good snapshot of the data.

This might be why its taking so long. Or perhaps its a really big database.

Veritas has oracle tools that lets you split a mirror and get a good snapshot of the data.

The way I get database backups is this:

Shutdown cold, take a copy, bring it back up.

But this takes time.

So you can shut down cold, split a mirror off, bring the database back up, mount the mirror, and take your cold backup off of that.

Then of course before the next backup you have to rebuild the mirror. This is at least possible with Mirror/UX.

SEP

[M. Tariq Ayub]

Hi,
If i am using online extension of omniback-II or data protector 5 then what will happen.

[Severus]

Hi Rajeev
I am using OV Data protector 5.0 with online extention. In this case what will be the time?

Faisal

[Severus]

Hi Rajeev
I am using OV Data protector 5.0 with online extention. In this case what will be the time?

Faisal

[Massimo Bianchi]

Hi,
the real question is what is the DB ?


I can talk about oracle.

For the restore of the files, then takne into account 1:1,5 ratio. If your backup lasted 10 hours, restore will last about 15 hours.


For the recovery (applying of logs): last recovery was using log of 300Mb ,and it took about 12 minutes foe each. It will depend on how many of them are generated in the meantime.

Massimo

[Robert-Jan Goossens]

Think about a hot backup from legato, I work with them for a couple off years, I know HP does not like it when I give info about a second party product but this is great !!!!!

Robert-Jan.

[Sunil Sharma_1]

Hi,
i can tell something about Oracle Database.
the recovery procedure in Oracle is like this
1. When we take online backup of oracle, it should be in hot backup mode.so nothing will be written to database and transaction will be stored in archive log files.
2. restore online backup.
3. apply the archive log files which generated during online backup.

But as you told time taken is very high so it may not be fisiable because lots of archive log files will get generated during this period.

Sunil

[Volker Borowski]

Hi,

talking about oracle....

It will not be 00:00 and it will not be 18:00 as well, and it will never be anything in between, because this RESTORE (it is not called RECOVER !!) will be inconsistent.

To become consistent the RESTORE needs to be RECOVERed afterwards (this is something completely diffrent). First of all, to be recoverable the backup needs to be done while tablespace are in BACKUP mode. Second: After all data is written to the tapes, you need to deactivate the backup mode. If you have several tablespaces, the first point of time which would be OK for a successfull consistent recovery is the exact last "END BACKUP" statement to your database. To reach it, you need to recover all archive logs untill this point if time. So if your backup ends at 18:00 and you issue the "END BACKUP" at 19:00:00:00:00, the first consistent time to be reached with this backup is 19:00:00:00:01 (!) no matter that your backup was already finished at 18:00 !

Talking about other databases: If running a filesystem backup of any kind is usually worthless. Usually thes databases have their own tools or APIs to create consisten online backups, which usually represent the exact end of the backup (i.e. SAPDB).

Hope this helps
Volker