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I have this ZFS box where I'm creating incremental snapshots, then piping them into RAR (4.2) for compression and encryption, and finally backing those files up remotely.

Thing is, RAR seems to ignore my setting to create volumes (i.e. a segmented archive) when doing so. I can't believe that this could be a limitation (can't see why feeding data via stdin would be any different from having RAR read data directly off the disk), so I'm thinking there's something else wrong with my approach.

Here's an example of me creating an archive:

zfs send filesystem@rev | rar a -m5 -md4096 -t -s -v5000000000b -ppassword -rr5 -sifilesystem@rev ~/filesystem@rev.rar

Any ideas why this doesn't segment my archive into 5GB parts? Instead I get, say, one big 44GB rar file.

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First thought is that if you were making the archive solid, rar would have no way to know "how solid" the final archive should be, since all data was added incrementally, not allowing rar to know at start the expected filesizes. –  Doktoro Reichard Aug 21 '13 at 15:33
    
Not sure what you mean by that... "How solid" it should be is not something RAR determines, it's something you tell it... Either way, it doesn't make any difference if I use solid archiving or not... Neither does recovery record, nor compression efficiency. I'm starting to think this is just a limitation in RAR. Perhaps I should use 7-zip instead. –  DanielSmedegaardBuus Aug 24 '13 at 17:24
    
To quote the readme file: Solid: An archive packed using a special compression method which sees all files as one continuous data stream. Particularly advantageous when packing a large number of small files. If you're feeding (continuous) data through a stream, rar would have no way to know about the file's details. Try the switch -s-. From what I read it is somewhat unclear whether enforcing -s or not results in a solid or partially solid archive. –  Doktoro Reichard Aug 24 '13 at 18:53
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Again, whether I use solid archiving or not makes no difference. Besides, per definition the archive created will become "solid" anyway, as it is one continuous data stream being fed to RAR. And solid archives support using segments when not using stdin. The solid archive behavior of RAR can be compared with using tar plus a compressor, except RAR uses clever sorting of source files, placing similar filetypes (text files, executable, etc.) together, thereby better utilizing the (limited) dictionary, (usually) achieving higher compression ratios. Either way, 7-zip works fine so I'll use that. –  DanielSmedegaardBuus Aug 26 '13 at 9:24

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