-------- Original Message --------
Subject: Re: Is it safe to mount subvolumes of already-mounted volumes
(even with different options)?
From: Sebastian Ochmann <ochm...@informatik.uni-bonn.de>
To: Chris Murphy <li...@colorremedies.com>, zhe.zhang.resea...@gmail.com
Date: 2014年07月17日 15:58
Hello,
I need to clarify, I'm _not_ sharing a drive between multiple
computers at the _same_ time. It's a portable device which I use at
different locations with different computers. I just wanted to give a
rationale for mounting the whole drive to some mountpoint and then
also part of that drive (a subvolume) to the respective computer's
/home mountpoint. So it's controlled by the same kernel in the same
computer, it's just that part of the filesystem is mounted at multiple
mountpoints, much like a bind-mount, but I'm interested in mounting a
subvolume of the already-mounted volume to some other mountpoint.
Sorry for the confusion.
Best regards
Sebastian
If you mean something like the following use case:
# mount /dev/sdb1 -o subvolid=257 /home
# mount /dev/sdb1 -o subvolid=5 /some/other/place
That is completly OK.
But when it comes to different mount option, especially different ro/rw
mount option,
although it is working for 3.16-rc*, the ro/rw mount option is still
under disscussion and the current rc implement
will cause a kernel warning mounting a subvolume rw when it's first
mounted as ro.
So in short:
1) mount subvolumes when the btrfs fs is already mounted.
Completly OK.
2) different mount option for different subvolume in one btrfs fs.
For most mount option including ro/rw, No.
Thanks,
Qu
On 17.07.2014 01:18, Chris Murphy wrote:
On Jul 16, 2014, at 4:18 PM, Sebastian Ochmann
<ochm...@informatik.uni-bonn.de> wrote:
Hello,
I'm sharing a btrfs-formatted drive between multiple computers and
each of the machines has a separate home directory on that drive.
2+ computers writing to the same block device? I don't see how this
is safe. Seems possibly a bug that the 1st mount event isn't setting
some metadata so that another kernel instance knows not to allow
another mount.
Chris Murphy
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