On Wednesday, December 17, 2014, Josh Durgin <josh.durgin@xxxxxxxxxxx> wrote:
On 12/17/2014 03:49 PM, Gregory Farnum wrote:
On Wed, Dec 17, 2014 at 2:31 PM, McNamara, Bradley
<Bradley.McNamara@xxxxxxxxxxx> wrote:
I have a somewhat interesting scenario. I have an RBD of 17TB formatted
using XFS. I would like it accessible from two different hosts, one
mapped/mounted read-only, and one mapped/mounted as read-write. Both are
shared using Samba 4.x. One Samba server gives read-only access to the
world for the data. The other gives read-write access to a very limited set
of users who occasionally need to add data.
However, when testing this, when changes are made to the read-write Samba
server the changes don’t seem to be seen by the read-only Samba server. Is
there some file system caching going on that will eventually be flushed?
Am I living dangerously doing what I have set up? I thought I would avoid
most/all potential file system corruption by making sure there is only one
read-write access method. Thanks for any answers.
Well, you'll avoid corruption by only having one writer, but the other
reader is still caching data in-memory that will prevent it from
seeing the writes on the disk.
Plus I have no idea if mounting xfs read-only actually prevents it
from making any writes to the disk; I think some FSes will do stuff
like defragment internal data structures in that mode, maybe?
-Greg
FSes mounted read-only still do tend to do things like journal replay,
but since the block device is mapped read-only that won't be a problem
in this case.
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Someone commented that the OS with the readonly mount will still do something potentially damaging to the filesystem at mount time. Something along the lines of replaying the xfs journal and the read write OS being unaware of it.
Jake
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