Thanks Dan. I think I get it now. One more question:
The size of the Gluster volume we want to create is 150TB. We are either
going to do a distribute only with 4 nodes or a distribute+repl2 with 8
nodes (depends on budget). Considering this, do you have any server ram
recommendations. The starting point is going to be 32GB, but should we
be thinking of 64 or 128?
-Scott
On 2/6/2014 7:07 PM, Dan Mons wrote:
Replies inline:
On 7 February 2014 10:11, Scott Dungan <scott@xxxxxxxxxxxxxxx> wrote:
I am new to Gluster and I am having a hard time grasping how Gluster
functions in distribute mode vs. distribute+replication. I am planning on
having 5 servers, with each server hosting a raid6-backed 36TB brick. For
simplicity, lets just pretend this is a 40TB brick. Here are my questions:
1. If I do a distribute configuration only, usable capacity of the Gluster
volume will be 5x40TB or 200TB?
Using "40TB" as a round number per brick:
distribute (no replicate) would be a single ~200TB GlusterFS volume.
2. In this configuration, what would clients see if one of the servers were
to fail?
Lots of errors. Typically, every fifth file or directory would be
missing, and you'd see lots of question marks in your "ls -l" output.
3. When the server comes back up, what steps would need to be taken to make
the Gluster volume consistent again?
In a distribute-only setup, there's no redundancy. So there's no
"consistency" so to speak. When the missing volume came online, the
files it holds would be available again.
4. if I do a distributed replicated (2) volume, will my usable capacity
become 160TB or 100TB, or perhaps something else entirely?
5 servers is an uneven amount of bricks. You'd end up with 120TB, but
40TB of that wouldn't be replicated. A 6th brick would solve that
problem, and you'd have ~120TB in full distribute+replicate(2).
5. In this configuration, one server may be removed for maintenance and the
file system stays consistent?
Theoretically yes. I try to keep my replicated brick downtime to a
minimum though. Similar to the ideas behind a RAID mirror, I don't
like running in production on only one copy of something for too long.
-Dan
--
Scott A Dungan
Senior Systems Administrator
Geological and Planetary Sciences
California Institute of Technology
Office: (626) 395-3170
Cell: (626) 993-4932
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