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Breaking up a large media set over multiple drives

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#1 SethR



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Posted 31 July 2017 - 07:42 PM

Not familiar enough with Retrospect to know if my proposed solution will or will not work for my problem.


I've been put in charge of a 19 tape media set that totals up to over 16TB in size. This media set is just one large backup originally made from a RAID many years ago. 


My boss asked me to restore the media set and gave me a stack of 3TB drives. Is it possible to do this restore in chunks and retrieve all the data or will I need to get large drives and build out a 16+TB raid to properly do the restore? The media set is filled with LTO4 tapes with about 800GB of data each on them. So my plan was to start with restoring tapes 1-3, then stop the restore and swap out the hard drives, mark those 3 as "missing" under the media set and then start a tape 4, do 4-6, then stop the restore and swap out the drives, lather, rinse, repeat. 


Is this a solution that will work? I wasn't sure if Retrospect ever wrote individual files to span across tapes and if this would leave me with multiple "incomplete" files on all the drives.



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#2 Lennart Thelander

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Posted 31 July 2017 - 08:19 PM

I'm afraid it will not work.


One solution is the one you outline yourself: Set up a 16 TB RAID and restore everything. That has two benefits: Everything will be in one place and you will read through the tapes only once.


Another solution is to select a group of folders at a time, so that each group adds up to (slightly) less than 3 TB and restore that to one of the destination drives. You might need to restore some files from each tape for each destination drive, making you go through all the tapes six times (six times 3TB is 18 TB, a bit more than the 16 you have.


You may optimize the latter solution by getting three 6 TB drives. First you make a Copy Backup operation from the tapes to a new Disk Media Set with the three drives as members. Then you do a restore of a group of folders from the Disk Media Set to the stack of 3 TB drives, one drive at a time. The cost of the three 6 TB drives will save probably save you a lot of tape swapping.


When finished, you can store those drives (or the tapes) off site as an extra insurance against data loss.

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