Re: What is needed for ZFS block cloning to work?

On Sat, Jul 11, 2026 at 3:35=E2=80=AFPM John F Carr <[email protected]> wrote:
>
> I enabled block cloning on 15.1-STABLE but copy_file_range
> between two files in the same directory does not cause
> bcloneused to change.  I have vfs.zfs.bclone_enabled=3D1
> and feature@block_cloning=3Denabled.  Is anything more
> needed?
>
> I looked at zfs_clone_range and zfs_freebsd_copy_file_range
> and saw nothing obvious that would make the copy fail.
>
> zpool list shows ALLOC changing by an amount similar to the
> size of the copied file.
>
> John Carr
>
>
> $ zpool get bcloneused data
> NAME  PROPERTY    VALUE        SOURCE
> data  bcloneused  0            -
> $ df .
> Filesystem   1K-blocks   Used     Avail Capacity  Mounted on
> data/scratch 104857600 129665 104727934     0%    /data/scratch
> $ truss -o /tmp/t cp IMG_6998.CR3 tmp2
> $ zpool get bcloneused data
> NAME  PROPERTY    VALUE        SOURCE
> data  bcloneused  0            -
> $ grep copy_file_range /tmp/t
> copy_file_range(0x3,0x0,0x4,0x0,0x7fffffffffffffff,0x0) =3D 33289458 (0x1=
fbf4f2)
> copy_file_range(0x3,0x0,0x4,0x0,0x7fffffffffffffff,0x0) =3D 0 (0x0)
> $ sysctl vfs.zfs.bclone_enabled
> vfs.zfs.bclone_enabled: 1
> $ zpool get feature@block_cloning data
> NAME  PROPERTY               VALUE                  SOURCE
> data  feature@block_cloning  enabled                local
>
> (kgdb) p zfs_bclone_enabled
> $1 =3D 1

IIRC the recsize property on the destination file system also needs to
match the record size of the source file (which is usually equal to
the source file system's recsize).  And there are also some
restrictions around copying to/from encrypted file systems.