[Gluster-users] Reconstructing files from shards

Jamie Lawrence jlawrence at squaretrade.com
Fri Apr 20 19:44:48 UTC 2018


So I have a volume on a gluster install (3.12.5) on which sharding was enabled at some point recently. (Don't know how it happened, it may have been an accidental run of an old script.) So it has been happily sharding behind our backs and it shouldn't have.

I'd like to turn sharding off and reverse the files back to normal.  Some of these are sparse files, so I need to account for holes. There are more than enough that I need to write a tool to do it.

I saw notes ca. 3.7 saying the only way to do it was to read-off on the client-side, blow away the volume and start over. This would be extremely disruptive for us, and language I've seen reading tickets and old messages to this list make me think that isn't needed anymore, but confirmation of that would be good.

The only discussion I can find are these videos[1]: http://opensource-storage.blogspot.com/2016/07/de-mystifying-gluster-shards.html , and some hints[2] that are old enough that I don't trust them without confirmation that nothing's changed. The video things don't acknowledge the existence of file holes. Also, the hint in [2] mentions using trusted.glusterfs.shard.file-size to get the size of a partly filled hole; that value looks like base64, but when I attempt to decode it, base64 complains about invalid input. 

In short, I can't find sufficient information to reconstruct these. Has anyone written a current, step-by-step guide on reconstructing sharded files? Or has someone has written a tool so I don't have to?



[1] Why one would choose to annoy the crap out of their fellow gluster users by using video to convey about 80 bytes of ASCII-encoded information, I have no idea.
[2] http://lists.gluster.org/pipermail/gluster-devel/2017-March/052212.html

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