Re: Question on RMAN restore from tape

From: Stefan Koehler <contact_at_soocs.de>
Date: Thu, 19 Dec 2019 11:58:20 +0100 (CET)
Message-ID: <2045950604.255998.1576753100806_at_ox.hosteurope.de>

Hello Andrea,

> In my experience, I see that rman will never tries to read the same "tape" in parallel. This is wise but this could limit your restore parallelism.

This can happen very easily if you change the parallelism / amount of channels between backup and restore. I have seen this a lot of times with IBM TSM and physical LTOs for example and the client was wondering why increasing the amount of channels did not speed up the restore.

Here is a simple example:

Backup with 2 RMAN sessions (because backup SLA is not as strict as restore)

---

Channel 1 writes to LTO tape 1 with: Backupset 1, Backupset 3 Channel 2 writes to LTO tape 2 with: Backupset 2, Backupset 4

Restore with 4 RMAN sessions (because restore SLA is more strict)

---

Channel 1 reads from LTO tape 1: Backupset 1
Channel 2 reads from LTO tape 2: Backupset 2
Channel 3 reads from LTO tape 1: Backupset 3 <<<< blocked because channel 1 already uses LTO tape 1
Channel 4 reads from LTO tape 2: Backupset 4 <<<< blocked because channel 2 already uses LTO tape 1

Best Regards
Stefan Koehler

Independent Oracle performance consultant and researcher Website: http://www.soocs.de
Twitter: _at_OracleSK

> Andrea Monti <ilsuonogiallo_at_gmail.com> hat am 19. Dezember 2019 um 11:29 geschrieben:
>
>
> Leng is right, but be careful
>  
>  - filesperset = alone will help and should always work but this might not be able to give you the best results
>  
>  - maxpiecesize or maxsetsize  will help you, too, but if you set them to "low" values your backups might suddenly start failing as the db start growing 
>  
>  - using section size to split big files' backups in several backuppieces might be the best choice 
>  
> In my experience, I see that rman will never tries to read the same "tape" in parallel. This is wise but this could limit your restore parallelism: you should double check the restore parallelism you can do by testing restore or double checking the "media ids" of your tapes
>  
> regards,
> Andrea

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Received on Thu Dec 19 2019 - 11:58:20 CET