[Gluster-users] DHT and NUFA

Amar Tumballi amar at gluster.com
Mon Mar 22 09:31:31 UTC 2010

> * for performance I want to read/write directly to the local volume.
> As DHT has no central metadata this should not give problems as long as
> the the data is on the right volume, correct?
That is correct.

> * The data is already distributed (in the unify/nufa setup) with a
> distributed hashing scheme. My initial idea was to hack my hashing scheme
> into Gluster so they would agree on where the data should be, but then I
> spotted a file nufa.c in the DHT directory. Does this mean I can use
> nufa with DHT? I can't find any documentation on this.
The 'nufa.c' you spotted in DHT directory is a development to get rid of old
'cluster/unify' module, which had a centralized namespace server which was
bottlenecking in scaling to more servers. (NOTE: there is another 'switch.c'
in dht directory, which should provide switch scheduler behavior).

Sorry about lesser documentation on this. But, yes, you can use nufa without
'cluster/unify' now, and you can still see all the data which were populated
with 'cluster/unify' earlier.

Define a nufa volume like below:

# instead of cluster/unify in volume write below volume
volume nufa
   type cluster/nufa
   option local-volume <volumename present in earlier nufa scheduler>
   option lookup-unhashed yes
   subvolumes <subvolumes list used in 'cluster/unify'>

> * Is there documentation about how DHT determines the location?
DHT determines the location based on a hashing algorithm. But when you use
NUFA, it tries to override the hashing logic with local-volume name in case
of create, but to find the file which is not in local subvolume, it will use
the same hashing algorithm used by dht.


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