Gluster users - Oct 2016 - How gluster parallelize reads

Hi to all.
I know that when writing, a client is writing to all replica at once,
thus the transfer rate is total_bandwidth/replica_count

But what about reads? Client is able to read from multiple nodes at
once? Which kind of data is reading?

Let me try to explain:

let's assume a 3MB file stored on 3 bricks on 3 servers (1 brick per
server). For semplicity, let's assume 1MB stored on each brick.

When client reads, will read the first MB from all of 3 servers in
parallel, then it moves to the secodn MB and so on, or is smart enough
to read the first MB from server1, the second from server2 and the
third from server3 at the same time?

I think that second case is way faster than first.

By default, the client reads from localhost first, if the client is also 
a server, or the first to respond. This can be tuned to balance the load 
better (see "gluster volume set help") but that's not necessarily
more
efficient. As always, it depends on the workload.

Reading as you suggested is actually far less efficient. The reads would 
always be coming from disk and never in any readahead cache.

On 10/03/2016 02:24 AM, Gandalf Corvotempesta wrote:
> Hi to all.
> I know that when writing, a client is writing to all replica at once,
> thus the transfer rate is total_bandwidth/replica_count
>
> But what about reads? Client is able to read from multiple nodes at
> once? Which kind of data is reading?
>
> Let me try to explain:
>
> let's assume a 3MB file stored on 3 bricks on 3 servers (1 brick per
> server). For semplicity, let's assume 1MB stored on each brick.
>
> When client reads, will read the first MB from all of 3 servers in
> parallel, then it moves to the secodn MB and so on, or is smart enough
> to read the first MB from server1, the second from server2 and the
> third from server3 at the same time?
>
> I think that second case is way faster than first.
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