Cool tool, but recommend reading the policies [0] section carefully, it did catch me off guard the first time I tried using it.<p>E.g. say you have /a/foo.txt and /b/foo.txt, and you run mergerfs /a:/b /merged<p>Now if you print or modify /merged/foo.txt, it would access /a/foo.txt because the default policy for file access is ff (first-found, as defined during the mount).<p>However, if you run "rm /merged/foo.txt", it would delete it from <i>both</i> /a and /b, because the default policy for unlink call would be "epall" (existing path, apply to all).<p>[0] <a href="https://github.com/trapexit/mergerfs#policy-descriptions" rel="nofollow">https://github.com/trapexit/mergerfs#policy-descriptions</a>
The "Why?" is hard to find, but I think this answer to "Why use mergerfs over unionfs" is informative:<p>> UnionFS is more like aufs than mergerfs in that it offers overlay / CoW features. If you're just looking to create a union of drives and want flexibility in file/directory placement, then mergerfs offers that, whereas unionfs is more for overlaying RW filesystems over RO ones.<p>Also:<p>> What should mergerfs NOT be used for?<p>1. databases: Even if the database stored data in separate files (mergerfs wouldn't offer much otherwise) the higher latency of the indirection will kill performance. If it is a lightly used SQLITE database then it may be fine but you'll need to test.<p>2. VM images: For the same reasons as databases. VM images are accessed very aggressively and mergerfs will introduce too much latency (if it works at all).<p>3. As replacement for RAID: mergerfs is just for pooling branches. If you need that kind of device performance aggregation or high availability you should stick with RAID.
Is this really a 'Show HN'? Anyway, I'm not affiliated with the maintainer either, but if it's of use to anyone reading I do maintain a Docker image for mergerfs:
<a href="https://github.com/OJFord/docker-mergerfs/" rel="nofollow">https://github.com/OJFord/docker-mergerfs/</a>
If you find this interesting then you might also be interested in SnapRAID: <a href="https://www.snapraid.it/" rel="nofollow">https://www.snapraid.it/</a><p>> SnapRAID is a backup program for disk arrays. It stores parity information of your data and it recovers from up to six disk failures.<p>> SnapRAID is mainly targeted for a home media center, with a lot of big files that rarely change.<p>> If the failed disks are too many to allow a recovery, you lose the data only on the failed disks. All the data in the other disks is safe.<p>I'm not affiliated with any of the projects.