ZFS subvolume support inside Bhyve vm

[Paul Vixie]

Pavel Odintsov wrote:
> Hello, Dear Community!
>
> I would like to ask about plans for this storage engine approach. I like
> ZFS so much and we are storing about half petabyte of data here.
>
> But when we are speaking about vm's we should use zvols or even raw file
> based images and they are discarding all ZFS benefits.

i use zvols for my bhyves and they have two of the most important zfs 
advantages:

1. snapshots.

> root at mm1:/home/vixie # zfs list|grep fam
> zroot1/vms/family    55.7G  3.84T  5.34G  -
> root at mm1:/home/vixie # zfs snap zroot1/vms/family at before
>
> [family.redbarn:amd64] touch /var/tmp/after
>
> root at mm1:/home/vixie # zfs snap zroot1/vms/family at after
> root at mm1:/home/vixie # mkdir /mnt/before /mnt/after
> root at mm1:/home/vixie # zfs clone zroot1/vms/family at before zroot1/before
> root at mm1:/home/vixie # fsck_ffs -p /dev/zvol/zroot1/beforep2
> ...
> /dev/zvol/zroot1/beforep2: 264283 files, 1118905 used, 11575625 free (28697 frags, 1443366 blocks, 0.2% fragmentation)
> root at mm1:/home/vixie # mount -r /dev/zvol/zroot1/beforep2 /mnt/before
> root at mm1:/home/vixie # mount -r /dev/zvol/zroot1/beforep2 /mnt/before
>
> root at mm1:/home/vixie # zfs clone zroot1/vms/family at after zroot1/after
> root at mm1:/home/vixie # fsck_ffs -p /dev/zvol/zroot1/afterp2
> ...
> /dev/zvol/zroot1/afterp2: 264284 files, 1118905 used, 11575625 free (28697 frags, 1443366 blocks, 0.2% fragmentation)
> root at mm1:/home/vixie # mount -r /dev/zvol/zroot1/afterp2 /mnt/after
>
> root at mm1:/home/vixie # ls -l /mnt/{before,after}/var/tmp/after
> ls: /mnt/before/var/tmp/after: No such file or directory
> -rw-rw-r--  1 vixie  wheel  0 Mar 10 22:52 /mnt/after/var/tmp/after

2. storage redundancy, read caching, and write caching:

> root at mm1:/home/vixie # zpool status | tr -d '\t'
>   pool: zroot1
>  state: ONLINE
>   scan: scrub repaired 0 in 2h24m with 0 errors on Thu Mar 10 12:24:13 2016
> config:
>
> NAME                                            STATE     READ WRITE CKSUM
> zroot1                                          ONLINE       0     0     0
>   mirror-0                                      ONLINE       0     0     0
>     gptid/2427e651-d9cc-11e3-b8a1-002590ea750a  ONLINE       0     0     0
>     gptid/250b0f01-d9cc-11e3-b8a1-002590ea750a  ONLINE       0     0     0
>   mirror-1                                      ONLINE       0     0     0
>     gptid/d35bb315-da08-11e3-b17f-002590ea750a  ONLINE       0     0     0
>     gptid/d85ad8be-da08-11e3-b17f-002590ea750a  ONLINE       0     0     0
> logs
>   mirror-2                                      ONLINE       0     0     0
>     ada0s1                                      ONLINE       0     0     0
>     ada1s1                                      ONLINE       0     0     0
> cache
>   ada0s2                                        ONLINE       0     0     0
>   ada1s2                                        ONLINE       0     0     0
>
> errors: No known data errors

so while i'd love to chroot a bhyve driver to some place in the middle 
of the host's file system and then pass VFS right on through, more or 
less the way mount_nullfs does, i am pretty comfortable with zvol UFS, 
and i think it's misleading to say that zvol UFS lacks all ZFS benefits.

-- 
P Vixie