[Gluster-users] Question on file reads from a distributed replicated volume

[Joe Julian]

Do, "gluster volume set help". There is a pretty good explanation of the read subvolume preferences and options. 

On April 10, 2015 6:56:27 PM PDT, Bharathram Sivasubramanian <Bharathram.Sivasubramanian at vantrix.com> wrote:
>Thanks, Krutika!
>
>
>So, if I understand you correctly...if both Brick 1 and Brick 2 have a
>good copy of the file, then we can't tell for sure if the file will be
>read only from Brick 1 all the time and not Brick 2? in other words,
>for read#1, the file could be read from brick 2 and for another read
>which could happen a few minutes later, the file could be read from
>brick 1?
>
>________________________________
>From: Krutika Dhananjay <kdhananj at redhat.com>
>Sent: Friday, April 10, 2015 9:30 PM
>To: Bharathram Sivasubramanian
>Cc: Gluster-users at gluster.org
>Subject: Re: [Gluster-users] Question on file reads from a distributed
>replicated volume
>
>
>
>________________________________
>From: "Bharathram Sivasubramanian"
><Bharathram.Sivasubramanian at vantrix.com>
>To: Gluster-users at gluster.org
>Sent: Saturday, April 11, 2015 3:03:48 AM
>Subject: [Gluster-users] Question on file reads from a distributed     
>  replicated volume
>
>Let us assume that we have a distributed replicated gluster volume with
>4 bricks. Brick 1 is replicating its data with Brick 2 and Brick 3 is
>replicating its data with Brick 4. Suppose a file called aa.txt is
>present and replicated on Bricks 1 & 2. A gluster client would like to
>read this file. Which brick will the file come from? In other words:
>
>-        Will the file always be fetched from brick 1?
>
>-        Will the file always be fetched from brick 2?
>
>-        Will the file be fetched from brick 1 or 2 depending on the
>attempt? i.e. is there some load balancing where sometimes the file
>comes from brick 1 and at other times the file will come from brick 2?
>
>A given file will consistently be "read" from one of the N (in this
>case 2) replicas, as long as it holds a good copy of the file (that
>which does not need heal), even with client restart. We call it the
>"read child" of the file. Load balancing within a volume is done across
>different files wherein different files would have different but
>constant read children.
>
>-Krutika
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>
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