Is there a way to set a default read node from a replicated volume?

[AltOscar]

Hello everyone!

First, some background:
I have a environment with 4 nodes in a replicated-distributed configuration. A,B and C,D nodes. A,B have X Y Z files and C,D have I J K files.
So, I've been doing some tests and found out that most of the time when im copying from gluster the file I, almost always it's sent from node D, but not always.

Why is this exactly? Is it random? From what I've read, there are some metrics that gluster uses, but couldn't quite put my finger on why exactly. Also, I was wondering if there's a way to always read from node D whenever I want to read files I J or K . Of course, if node D is down, it'll read from node C.

Thank you for your answers and sorry for my english, It's not my mother tongue.

Best regards

[aravindavk]

Where the volume is mounted? outside node other than A, B, C and D or mounted in D?

[aravindavk]

If the Client mounts the Volume by using the "D" node then it may read from the same node if a good copy is available. Try by setting gluster volume set <volname> cluster.choose-local off.

[AltOscar]

So what I'd like to do is as follows:
Client mounts the volume by using the "A" node (so neither C or D). What I'd like to do (idk if it's even posible) is to set the "D" node as default for reading. So whenver the client wants to acces the J file, It'll be copied from D node, not C. (unless D node is down).

Thank you for your answers and time!

[AltOscar]

Hello everyone!
I've been running tests and as I said on my first comment, it seems random still.

What I'd like to do is, from a cliente outside any node, to read from node D by default, so unless node D is down it'll read files from node D and not from node C

Any thoughts?

[itisravi]

There is cluster.read-subvolume option that you can set, e.g. gluster volume set $volname read-subvolume $volname-client-1
but it works only for plain replicate volumes.

For distributed-replicate, you need to manually edit the fuse volfile and adjust the values such that each replica has the desired value, eg. option read-subvolume testvol-client-0 for the 1st replica pair, option read-subvolume testvol-client-3 for the 2nd replica pair etc. The fuse clients will need to be remounted for it to take effect.

If you always want to select tje same 'n'th brick in every replica pair, you can set the read-subvolume-index option. See gluster volume set help for more details.

[AltOscar]

read-subvolume-index Did the trick, thank you so much!!