Gluster users - Apr 2015 - Question on file reads from a distributed replicated volume

----- Original Message -----
> 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 
> _______________________________________________
> Gluster-users mailing list
> Gluster-users at gluster.org
> http://www.gluster.org/mailman/listinfo/gluster-users
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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
_______________________________________________
Gluster-users mailing list
Gluster-users at gluster.org
http://www.gluster.org/mailman/listinfo/gluster-users

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