Comparison to ZFS and BTRFS

[Demi Marie Obenour <demi@invisiblethingslab.com>]

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How does bcachefs manage to outperform ZFS and BTRFS?  Obviously being
licensed under GPL-compatible terms is an advantage for inclusion in
Linux, but I am more interested in the technical aspects.

- How does bcachefs avoid the nasty performance pitfalls that plague
  BTRFS?  Are VM disks and databases on bcachefs fast?
- How does bcachefs avoid the dreaded RAID write hole? 
- How does an O_DIRECT loop device on bcachefs compare to a zvol on ZFS?
- Is there a good description of the bcachefs on-disk format anywhere?
- What are the internal abstraction layers used in bcachefs?  Is it a
  key-value store with a filesystem on top of it, the way ZFS is?
- Is it possible to shrink a bcachefs filesystem?  Does bcachefs have
  any restrictions regarding the size of disks in a pool, or can I just
  throw a bunch of varying-size disks at bcachefs and have it spread the
  data around automatically to provide the level of redundancy I want?
- Can bcachefs use faster storage as a cache for slower storage, or
  otherwise move data around based on usage patterns?
- Can bcachefs saturate your typical NVMe drive on realistic workloads?
  Can it do so with encryption enabled?
- Is support for swap files on bcachefs planned?  That would require
  being able to perform O_DIRECT asynchronous writes without any memory
  allocations.
- Is bcachefs being used in production anywhere?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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