Shared disk library - restore

  • 2 February 2022
  • 5 replies

Badge +7



I have a question regarding magnetic disk library setup and how will it affect restores.


So what is being in the thoughts:

  1. Library has for example 4 media agents assigned to it;
  2. Each media agent would have own mount path provided from SAN;
  3. We would then share mount paths between media agents (exportfs (NFS..))
  4. Local to media agent mount path would have Read/Write access and other media agents who have that mount path as a shared one would have Read access
  5. Transport Type would be Regular
  6. Mount paths would have spill and fill for load balancing


With this setup a question came: what will happen if backup_1 was backed up into media_agent_1 out of 4 media agents used in that library, and this media agent is offline - can we still restore data from backup_1 with other 3 remaining media agents? At this point looks like a no - because mount paths to which backup_1 has been done is offline, so how can other media agents in the library be used for a restore?


Can this work? If not - can you suggest something from your view?


Best answer by Jordan 2 February 2022, 22:32

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5 replies

Userlevel 5
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Hi @benjaminas 


This setup will work however consider below:

  • if using deduplication, most likely no restores will work if ANY 1 of the media agent’s is offline for any reason as deduplication will reference previously written data against the library and chances are, required blocks are spread across all 4 mount paths.
  • if not using deduplication, restore will not work for job that wrote to the path local to the offline media agent, all other restores against online media agents will work


If all media agents are always online then you would have no issues. 


Thank you

Badge +7

@Jordan ,


would there be some better solution for disk library that has redundancy for restore purposes, or this is just how it is?



Userlevel 5
Badge +11

You can use a NAS rather than SAN. That way all mount paths are accessible by all media agents, thus providing redundancy. Downside is that performance may not be as good as SAN since it’ll be over LAN. 

Badge +7

OK, so with SAN we pretty much rely on having each media agent in the library online at all times for a successful restore. 

Thanks for confirming. 

Userlevel 5
Badge +11

Yes, that is correct.


This is a hardware limitation.


No problems at all.