[Gluster-users] read consistency amongst bricks / sync writes

Whit Blauvelt whit.gluster at transpect.com
Tue Apr 19 16:21:30 UTC 2011

On Tue, Apr 19, 2011 at 06:00:28PM +0200, Vincent Thomasset wrote:

> My idea is currently to run it on the same machines in the cluster that
> actually need storage, so that each machine would indeed use a local
> mount, so that i could reuse the existing, and large, storage space
> available without hassle (one of the things that make glusterfs pretty
> cool to deploy on existing clusters IMO).
> But i don't see how this could be a problem, isn't the glusterfs mount the
> so called native client method or did i get the doc wrong ?

You can have the local mount be directly as ext3/4, in which case gluster
doesn't replicate simultaneously when you write to it. Or you can also have
the local mount be "-t glusterfs", in which case it does. At least in my

So I have a machine that's half a gluster mirror with a directory at
/mnt/somedir that's formatted ext4 and given to gluster. Then gluster is
exporting the filesystem as /somedir (because I reused the name), and it can
be locally mounted with:

  mount -t glusterfs localhost:/somedir /mnt/tmp

Now if I look at my filesystems with df I get

                       309637120 118580172 175328308  41% /mnt/somedir
  localhost:/somedir   309637120 118580224 175328256  41% /mnt/tmp

(That first is because gluster's using a filesystem on an lvm in my case.)

Both /mnt/somedir and /mnt/tmp have the same files in them. But anything I
write to /mnt/tmp/ gets instantly replicated to the mirror, because it's
going through the gluster client handling the mount. Anything I write to
/mnt/somedir does not get instantly replicated, because it's mounted
directly, without gluster being aware of what I'm doing until something
triggers gluster later to look at that particular file.


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