[Bugs] [Bug 1316234] New: Feature request to manipulate DHT on local mount to force writing to local storage

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1316234

            Bug ID: 1316234
           Summary: Feature request to manipulate DHT on local mount to
                    force writing to local storage
           Product: GlusterFS
           Version: mainline
         Component: libglusterfsclient
          Assignee: bugs at gluster.org
          Reporter: dandenson at gmail.com
                CC: bugs at gluster.org



Description of problem:
When mounting a gluster volume, can't dictate that writes will be local

Version-Release number of selected component (if applicable):
future mainline

How reproducible:
n/a

Steps to Reproduce:
1.n/a

Additional info:

Consider this use case.  Want to have a single visible volume across storage
bricks *but* not distribute files on write.

There are a number of Network Video Recorders (NVR).  Each NVR, needs to write
to local storage.  Each NVR needs to read from all NVR cluster members so that
it can display video incidents in it's UI.  There is a database storing
metadata, but that can easily be synced w/ db native tools.

Additionally, some of the NVR might be across relatively slow WAN-vpn or
point-to-point links.

DHT hash distribution would saturate those links, while providing nothing
useful to each individual NVR.  By using gluster to distribute the volume, each
NVR can read and write to a single file store. 

Allowing a volume option like dht.writelocalhost or simply dht.disable 'true'
would fit this use case perfectly.


This can be simulated with 2 nodes and nfs+aufs.  On nvr1, mount
nvr2:/datastore via nfs to /mnt/nvr2_datastore
mount.aufs -o br=/local_datastore=rw:/mnt/nvr2_datastore=rw none
/mnt/aufs_datastoreview.
writes to the aufs mountpoint happen locally but can see remote writes via the
underlaid nfs mountpoint.



This can be 'hacked' with gluster
/local_datastore
gluster volume create gluster_datastore
nvr1:/local_datastore,nvr2:/local_datastore
use aufs as above, but with /mnt/gluster_datastore instead of
/mnt/nvr2_datastore.

aufs writes to /local_datastore, but underlays the gluster_datastore.  because
it's 'rw' aufs allows deletes first on local_datastore, then passes through to
gluster_datastore.

This actually works, but writing into a gluster brick directly isn't a
'production option'


ultimate goal: write local, read and delete local+global.

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