[Mayzie]

> I don't know if this exists or not, but I'd like to try something like a fuse filesystem which can transparently copy a file to a fast scratch SSD when it is first accessed.

You may be interested in checking out bcache[1] or bcachefs[2].

[1] https://www.kernel.org/doc/html/latest/admin-guide/bcache.ht...

[2] https://bcachefs.org/

[theblazehen]

lvm-cache works as well, if you're already using LVM.

https://github.com/45Drives/autotier is exactly what they were asking for as well

[magicalhippo]

I've done some testing with using ZFS on top of LVM with dm-writecache.

Worked well enough on the small scale, but sadly haven't had the time or hardware to test it in a more production-like environment.

Also, it was starting to feel a bit like a Jenga tower, increasing the chances of bugs and other weird issues to strike.

[kaliszad]

I wouldn't recommend combining those two. It's only begging for problems.

[magicalhippo]

Yeah that's my worry. Still, got 6x old 3TB disks that still work and a few spare NVMEs, so would be fun to try it for teh lulz.

[kaliszad]

Rather build a L2ARC or metadata special device hybrid setup using ZFS or skip ZFS and go for lvmcache/ mdadm style RAID with XFS or something.

[magicalhippo]

But L2ARC only helps read speed. The idea with dm-writecache is to improve write speed.

I started thinking about this when considering using a SAN for the disks, so that write speed was limited by the 10GbE network I had. A local NVMe could then absorb write bursts, maintaining performance.

That said, it's not something I'd want to use in production that's for sure.

There was some work being done on writeback caching for ZFS[1], sadly it seems to have remained closed-source.

[1]: https://openzfs.org/wiki/Writeback_Cache

[hamandcheese]

My assumption with bcache is that it operates on blocks rather than entire files. Am I wrong?

[LtdJorge]

Yeah, bcache is exactly that