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

[Bharathram Sivasubramanian]

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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