Posted Apr 9, 2009 15:09 UTC (Thu) by ESRI (guest, #52806)
We loopback mount all the ISO's, then union these filesystems together to "recreate" the appearance of one tree with everything in it, then are able to export all of this via NFS to clients. We now have the raw .iso files available, each disk individually as well as a merged tree.
This probably isn't the most typical use case for unioning :-) It works, but is rather slow as you might imagine... and our /etc/exports file is very ugly indeed!
Posted Apr 9, 2009 16:09 UTC (Thu) by kfiles (subscriber, #11628)
That would solve your use case, where you really just want a union mount to implement logical volumes, not true FS overlay with transparent write-through.
Posted Apr 9, 2009 19:26 UTC (Thu) by jblunck (subscriber, #27345)
Posted Apr 9, 2009 19:20 UTC (Thu) by jblunck (subscriber, #27345)
Posted Apr 9, 2009 19:53 UTC (Thu) by ESRI (guest, #52806)
Posted Apr 9, 2009 19:24 UTC (Thu) by vaurora (guest, #38407)
Remember the source control use case for original Plan 9 and BSD union mounts - you don't actually want a union mount, you want a full-fledged source control system.
Posted Apr 9, 2009 23:16 UTC (Thu) by vaurora (guest, #38407)
Clearly, this works since it is what BSD has been doing for years. But I don't like the idea of caching the entire directory very much. Dealing with directories with lots of entries is often not ideal, and this will add another constraint on the size of directories. For small directories, this works fine. For large directories, suddenly the size of directories is related to the amount of memory you have available. Imagine not being able to do an ls because you don't have enough memory to process the whiteouts - which you could fix if you could delete some files - but you don't know what the files are named because readdir() fails...
I'm sure you've thought about this more than I have, though. Any thoughts?
Posted Apr 11, 2009 5:14 UTC (Sat) by bharata (subscriber, #7885)
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