Date: Sat, 27 Dec 2014 14:19:05 +0000 From: Steven Hartland <killing@multiplay.co.uk> To: freebsd-fs@freebsd.org Subject: Re: ZFS: Mount partition from ZVOL with volmode=dev Message-ID: <549EBFD9.8090407@multiplay.co.uk> In-Reply-To: <32BEFAB7-936E-42F0-AE75-FB978C13885C@gmail.com> References: <91E1211B-7E84-472B-8098-630AE8C97251@gmail.com> <32BEFAB7-936E-42F0-AE75-FB978C13885C@gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 27/12/2014 13:18, Paul Chakravarti wrote:
>> On 26/12/2014 23:54, Paul Chakravarti wrote:
>>> Hello,
>>>
>>> I am using a ZVOL configured with 'volmode=dev' 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’t show up under /dev/zvol as separate devices with
>>> 'volmode=dev' 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=dev 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’t exposed to geom.
That's exactly what volmode=dev does, if you want geom ones don't
specify volmode.
> On the host system:
>
> # zfs create -V10G -o volmode=dev 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
> => 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
> UFS partition on the host with volmode=guest - with volmode=default (ie. geom
There is no volmode=guest, where did you get that from?
> when vfs.zfs.vol.mode=1) 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’t 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
> rc.conf parameters before passing to bhyve)
>
> volmode=default | 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=default (geom - vfs.zfs.vol.mode=1) 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=dev.
What error do you get?
Regards
Steve
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?549EBFD9.8090407>