Re: Remove a brick, rebuild it, put it back in

Sergei Gerasenko <sgerasenko74@xxxxxxxxx> · Mon, 10 Oct 2016 16:31:06 -0500

To answer my own question. I now realize the importance of creating specifically directories and not files because it appears that directories are created on each pair regardless of the hash. And so, if a host is down, changes will be marked as pending for that host. With files it's different because in that case the name of the file IS important resulting in the file being placed on only 1 pair.

On Mon, Oct 10, 2016 at 3:47 PM, Sergei Gerasenko <sgerasenko74@xxxxxxxxx> wrote:
The guide here: https://gluster.readthedocs.io/en/latest/Administrator%20Guide/Managing%20Volumes/#replace-faulty-brick suggests running the following while the partner host is down:

mkdir /mnt/r2/<name-of-nonexistent-dir>
rmdir /mnt/r2/<name-of-nonexistent-dir>
setfattr -n trusted.non-existent-key -v abc /mnt/r2
setfattr -x trusted.non-existent-key  /mnt/r2

That should set an extended attribute on the healthy replica partner indicating that there are pending changes for the partner host.

Remembering that we're in a distributed, replicated situation, I don't quite understand because the created directories can be created on any pair, not necessarily the one we're fixing. I think the name of the directory should chosen such that its dht value lands the file on the affected brick (the healthy of the two replicate hosts). That's not easy to do.

Does somebody have any suggestions?

On Thu, Oct 6, 2016 at 10:47 PM, Sergei Gerasenko <sgerasenko74@xxxxxxxxx> wrote:
Step 10 isn't really necessary. The changes should probably be monitored under the brick directory.

On Thu, Oct 6, 2016 at 10:25 PM, Sergei Gerasenko <sgerasenko74@xxxxxxxxx> wrote:
I've simulated the problem on 4 VMs in a distributed replicated setup with a 2 replica-factor. I've repeatedly torn down and brought up a VM from a snapshot in each of my tests.

What has worked so far is this:

Make a copy of /var/lib/glusterd from the affected machine, save it elsewhere.
Configure your new machine (in my case I reverted to a VM snapshot). Assign the same ip and hostname!
Install gluster.
Stop the daemons if they are running.
Nuke the /var/lib/glusterd directory and replace it with the saved copy in step 1.
Create the brick directory.
Get the extended volume attribute from a healthy node like so: getfattr -e base64 -n trusted.glusterfs.volume-id /data/brick_dir
Apply the extended attribute volume id attribute like so: setfattr -n trusted.glusterfs.volume-id -v 'the_value_you_got_in_7==' /data/brick_dir
Start the daemons.
FUSE mount the gluster partition through the daemons running locally. So the /etc/fstab would contain something like: localhost:/gluster_volume /mnt/gluster  glusterfs _netdev,defaults  0 0
On the healthy partner machine with another fuse mount point to the same volume do something like: find /mnt/fuse | xargs stat.
Step 8 will make files appear under the mount point on the new box but the files are not going to be physically in the brick directory -- yet. See 10.
Run the heal command from the same host where you ran find. That will finally sync the files to the brick. Run the heal info command periodically and the number of files being healed should eventually go down to 0. 
That's my experience with the VMs today.

On Wed, Oct 5, 2016 at 4:46 PM, Joe Julian <joe@xxxxxxxxxxxxxxxx> wrote:
What I always do is just shut it down, repair (or replace) the brick, then start it up again with "...  start $volname force". 

On October 5, 2016 11:27:36 PM GMT+02:00, Sergei Gerasenko <sgerasenko74@xxxxxxxxx> wrote:
Hi, sorry if this has been asked before but the documentation is a bit conflicting in various sources on what to do exactly.

I have an 6-node, distributed replicated cluster with a replica factor of 2. So it's 3 pairs of servers. I need to remove a server from one of those replica sets, rebuild it and put it back in.

What's the tried and proven sequence of steps for this? Any pointers would be very useful.

Thanks!
  Sergei

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