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I reinstalled my laptop with btrfs on / because "why not" about a year ago. I ran into issues with maintaining a huge ~1M file Maildir, it seemed to do very ba

by avar 10y ago

I reinstalled my laptop with btrfs on / because "why not" about a year ago. I ran into issues with maintaining a huge ~1M file Maildir, it seemed to do very badly with huge directories. Some kernel thread would be at 99% CPU while I was trying to populate a Maildir, and the entire system ground to a halt. More importantly I would run into issues like running out of space on / with 20G left, but it was the "wrong kind of space". I.e. I had run out of metadata space but had plenty of file space left and had to run a rebalancing operation on the filesystem. I didn't need any of the COW etc. advanced features that btrfs provides, and didn't test them, but as just a normal user needing a general purpose filesystem it was a bit too much hassle, especially with needing to administer the filesystem in a manner similar to how I might administer a RDBMS. I ended up just going back to ext4.

tadfisher 10y ago
A subvolume for your Maildir, mounted with "-o nodatacow", would have prevented the first issue. If btrfs could modify that behavior automatically using heuristics it would truly be general-purpose. However there are some inherent tradeoffs of that approach that users need to consider, and I consider that downside a basic constraint of the Unix filesystem abstraction.
- avar 10y ago
  I think I did try stuff like that, including mounting / with nodatacow and other similar options. I walked away with the impression that btrfs was a powerful tool for certain use-cases, but definitely not something I'd call a "general purpose" filesystem given the need to be fairly knowledgeable about its internals to use it for common desktop use-cases. To me a general purpose filesystem is something like ext4, it doesn't have amazing performance, it's not bad either, but generally nothing unexpected happens with it and I can just leave it there and don't have to worry about it. The btrfs filesystem seemed like the opposite of that. A very powerful tool whose power and flexibility made it less general purpose by virtue of needing to keep close tabs on how you were using it.
  - ryao 10y ago
    If you are open to trying again, I suggest trying ZFS. It should work well here.
- ryao 10y ago
  nodatacow means no checksums. Whatever performance problem it was intended to resolve should also recur the moment that a snapshot is done, because then CoW re-enters the picture.

by avar 10y ago

tadfisher 10y ago

A subvolume for your Maildir, mounted with "-o nodatacow", would have prevented the first issue. If btrfs could modify that behavior automatically using heuristics it would truly be general-purpose. However there are some inherent tradeoffs of that approach that users need to consider, and I consider that downside a basic constraint of the Unix filesystem abstraction.

avar 10y ago
I think I did try stuff like that, including mounting / with nodatacow and other similar options. I walked away with the impression that btrfs was a powerful tool for certain use-cases, but definitely not something I'd call a "general purpose" filesystem given the need to be fairly knowledgeable about its internals to use it for common desktop use-cases. To me a general purpose filesystem is something like ext4, it doesn't have amazing performance, it's not bad either, but generally nothing unexpected happens with it and I can just leave it there and don't have to worry about it. The btrfs filesystem seemed like the opposite of that. A very powerful tool whose power and flexibility made it less general purpose by virtue of needing to keep close tabs on how you were using it.
- ryao 10y ago
  If you are open to trying again, I suggest trying ZFS. It should work well here.
ryao 10y ago
nodatacow means no checksums. Whatever performance problem it was intended to resolve should also recur the moment that a snapshot is done, because then CoW re-enters the picture.