[Gluster-users] rebalance and volume commit hash

Piotr Misiak pmisiak at cloudferro.com
Mon Jan 16 12:53:33 UTC 2017


Can you tell me please why every volume rebalance generates a new value
for the volume commit hash?

If I have fully rebalanced cluster (or almost) with millions of
directories then rebalance has to change DHT xattr for every directory
only because there is a new volume commit hash value. It is pointless in
my opinion. Is there any reason behind this? As I observed, the volume
commit hash is set at the rebalance beginning which totally destroys
benefit of lookup optimization algorithm for directories not
scanned/fixed yet by this rebalance run.

I'm also curious what is happening during file lookup. As I know DHT
hash ranges are stored only in DHT xattr on every brick.
If gluster needs to find on which brick the file is located, it has to
read DHT xattr from every distribute brick to build complete hash ring.
Am I right?
I suppose this information is then cached but for how long and how big
is this cache, is it configurable?


Piotr Misiak
Senior Cloud Engineer
CloudFerro Sp. z o.o.

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