Date: Sat, 27 Dec 2014 13:18:32 +0000 From: Paul Chakravarti <paul.chakravarti@gmail.com> To: freebsd-fs@freebsd.org Subject: Re: ZFS: Mount partition from ZVOL with volmode=dev Message-ID: <32BEFAB7-936E-42F0-AE75-FB978C13885C@gmail.com> In-Reply-To: <91E1211B-7E84-472B-8098-630AE8C97251@gmail.com> References: <91E1211B-7E84-472B-8098-630AE8C97251@gmail.com>
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>On 26/12/2014 23:54, Paul Chakravarti wrote:
>> Hello,
>>
>> I am using a ZVOL configured with 'volmode=3Ddev' as the virtio disk =
device for
>> a bhyve instance (which works fine) but was trying to workout whether =
there
>> was any way of mounting the underlying partitions on the host system =
- the
>> partitions don=E2=80=99t show up under /dev/zvol as separate devices =
with
>> 'volmode=3Ddev' so was wondering is there is any other way of getting =
at these
>> other than mounting in a bhyve instance?
>>
>> Thanks, Paul
> I cant reproduce this on HEAD r276067
>
> zfs create -V 8192 -o volmode=3Ddev tank/tvol
> root at head:src> ls -l /dev/zvol/tank/
> total 0
> crw-r----- 1 root operator 0x85 Dec 27 00:08 tvol
>
> Regards
> Steve
Hi,
Sorry - I should have been clearer. The zvol shows up on the host
system but the partitions aren=E2=80=99t exposed to geom.
On the host system:
# zfs create -V10G -o volmode=3Ddev tank/vps/vm0
# zfs list -o name,used,volmode tank/vps/vm0
NAME USED VOLMODE
tank/vps/vm0 10.3G dev
# ls -l /dev/zvol/tank/vps/
total 0
crw-r----- 1 root operator 0x7b Dec 27 13:30 vm0
The zvol mounted on the bhyve guest:
# bhyveload -c /dev/nmdm0A -m 512M -d /dev/zvol/tank/vps/vm0 vm0
# bhyve -c 2 -m 512M -A -H -P -s 0:0,hostbridge -s =
1:0,virtio-net,tap0 -s 2:0,lpc -s 3:0,virtio-blk,/dev/zvol/tank/vps/vm0 =
-l com1,/dev/nmdm0A vm0
On the bhyve guest this shows up as a geom device:
root@vm0:~ # geom disk list
Geom name: vtbd0
Providers:
1. Name: vtbd0
Mediasize: 10737418240 (10G)
Sectorsize: 512
Mode: r2w2e3
descr: (null)
ident: BHYVE-747A-2A76-FAC
fwsectors: 0
fwheads: 0
And is partitioned in the guest as follows:
root@vm0:~ # gpart show -p
=3D> 34 20971453 vtbd0 GPT (10G)
34 1024 vtbd0p1 freebsd-boot (512K)
1058 19919872 vtbd0p2 freebsd-ufs (9.5G)
19920930 1048576 vtbd0p3 freebsd-swap (512M)
20969506 1981 - free - (991K)
What I am trying to work out is whether there is any way I can mount the =
guest=20
UFS partition on the host with volmode=3Dguest - with volmode=3Ddefault =
(ie. geom
when vfs.zfs.vol.mode=3D1) the device does show up as a geom provider =
and you can
just mount the partition from /dev/vol directly. The ZFS man page =
suggests that
you can=E2=80=99t but given that you can clearly mount from within a VM =
was wondering
is there is any way round this on the host (I am trying to clone a disk =
device
to run multiple bhyve instances but want to mount and modify some of the=20=
rc.conf parameters before passing to bhyve)
volmode=3Ddefault | geom | dev | none
This property specifies how volumes should be exposed to the =
OS.
Setting it to geom exposes volumes as geom(4) providers, =
providing
maximal functionality. Setting it to dev exposes volumes only =
as
cdev device in devfs. Such volumes can be accessed only as raw =
disk
device files, i.e. they can not be partitioned, mounted, =
participate
in RAIDs, etc, but they are faster, and in some use scenarios =
with
untrusted consumer, such as NAS or VM storage, can be more =
safe.
Volumes with property set to none are not exposed outside ZFS, =
but
can be snapshoted, cloned, replicated, etc, that can be =
suitable for
backup purposes. Value default means that volumes exposition =
is con-
trolled by system-wide sysctl/tunable vfs.zfs.vol.mode, where =
geom,
dev and none are encoded as 1, 2 and 3 respectively. The =
default
values is geom. This property can be changed any time, but so =
far it
is processed only during volume creation and pool import.
Using volmode=3Ddefault (geom - vfs.zfs.vol.mode=3D1) causes the =
installer to fail
when you try to create a UFS filesystem under bhyve - it is possible to =
get
round this by creating the partitions manually but my preference would =
be to
use volmode=3Ddev.
Paul
=20
=20=
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