[bug] ZFS zvol dev entry disappearing upon reboot

McLone mclone at gmail.com
Sat Jul 18 17:56:25 UTC 2009

Hell Low.

As downloading torrent files from many peers to ZFS
imposes fragmentation (and there's no way to defragment
ZFS volume - what a pity! How come now-a-days FS can
go like this?), i created zvol with UFS2 on it last time
i wanted to watch some old sci-fi. I had plans to
move sci-fi from UFS2/zvol to ZFS when it'll be complete,
but forgot it, and rebooted machine. After reboot
rtorrent said sci-fi is marked as complete, but it
can not find files. I wasn't surprised, as i haven't modified
my /etc/fstab, so i entered "mount /dev/zvol" and pressed
Tab in hope of tcsh (eek) autocomplete.
It just beeped on me.
I've done "ls /dev" and there was no directory there named zvol.
Then i've done "zfs list" and my zvol was there.
Puzzled, i've done "zfs snapshot" and then a little dance of
"zfs send | zfs recv" to a new volume. Now dev entries appeared
(both for newly created snapshot of an old zvol and for new zvol).
I rebooted, and there was no /dev/zvol again.

I looked at my uname -v output (it was HEAD/amd64 from Jul 1)
and decided to update. Updating didn't solved this problem.

Strangely, simple "zfs rename zpool/zvol zpool/newzvol"
cures this woe, but i think this is a bug.

Steps to reproduce:
zfs create -V 1g zpool/zvol
[newfs /dev/zvol/zpool/zvol]
ls /dev

zfs rename zpool/zvol zpool/newzvol
mount /dev/zvol/zpool/zvol /mnt
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