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We plan to use two tape libraries (one 48 slot and one smaller 8 slot). The 48 slot will be used to write data (~50+TB/annum), once the data has been written and cartridges become full we plan to remove the cartridges and put them in an offline storage facility.

Once some data is required, we plan to take the cartridge and put it into the smaller tape library to retrieve the data.

Will the other tape library "know" what data is stored in the tape? Do tape's store information about the files that are stored in them as well?

We plan to use LTO-5 (but not with LTFS).

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this question is about the backup software used. Make sure both drives use same kind of tapes. Modern software may require you to insert several cartridges in order to recover a specific file. –  anttiR Nov 9 '11 at 10:32

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The secondary tape library (more specifically the backup software on the secondary system) will not know the contents of the tapes because the backup software on the secondary system has not written the data to the tapes and therefore has no catalog of the data written to those tapes (the catalog is the file by file "record" of the data that's been written to the tapes). In order to restore data from the tapes on the secondary system, you'll need to catalog the tapes, which will perform a file by file catalog of all of the data on the tapes, which could take a considerable amount of time depending on how much data is written to the tape.

I don't know what backup software you're using but in Symantec BackupExec you can schedule a Catalog job, so that might be a way to automate the catalog operations. Incidentally, you can import a catalog from one BE server to another.

http://www.symantec.com/business/support/index?page=content&id=TECH68896

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Both tape libraries are connected to a single backup software, more specifically EMC Networker. I have determined that taking the media out from one tape library into another will not destroy the data, as the label associated with the cartridge will be "known" to the Networker server –  Irfan Nov 10 '11 at 16:48

Just to close this thread, I'll answer my own question:

I have tested EMC Networker with two Dell Powervault TL4000 tape libraries, and it does support tape mobility because the tape label is consistent and Networker stores archive data locations against tape labels.

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Most backup programs that I have come across can import tapes and will simply require you to catalog them. However this is assumed to be a oneway process and can get in a real mess if you try to move tapes back and forth without wiping them in between.

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Our scenario would use a single backup management software, but essentially two tape libraries. Is it possible to take a tape out form one library and insert it into another. Will the software still be able to retrieve the data? –  Irfan Nov 9 '11 at 11:28
    
I don't believe that importing media is a destructive process and nothing I can find in my backup software documentation suggests that it is. –  joeqwerty Nov 9 '11 at 18:26
    
No, I wasn't suggesting it was, however it can screw up the catalog on the backup server in the two leading backup softwares. Of course this can be recovered by recataloguing all your tapes, but do you want to go through that PITA when it can be simply avoided? –  JamesRyan Nov 10 '11 at 11:12
    
Bear in mind I am talking about when you add or change data on the tape rather than read only. –  JamesRyan Nov 10 '11 at 12:32
    
@JamesRyan: Gotcha. Thanks for the clarification. –  joeqwerty Nov 10 '11 at 17:12

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