Re: Increasing replica count from 2 to 3

[Jackie Tung <jackie@xxxxxxxx>]

Ravi,

Got it thanks.  I’ve kicked this off, it seems be doing OK.

I am a little concerned about a slow creep of memory usage:

* swap (64GB) completed filled up on server_1

* general memory usage creeping up slowly over time.

$ free -m

              total        used        free      shared  buff/cache   available

Mem:         128829       55596         614          53       72618       71783

Swap:         61034       61034           0

Similar issue on server_2, though lower starting memory usage:

The “available” number is slowly going down - at this rate, probably will go to 0 before heal is done.

We are actually running 3.8.6, I’d like to try to pause the heal, upgrade to 3.8.7, and resume.  Is this possible heal suspend/resume possible or advisable?

The upgrade idea came from this on bugzilla (not 100% if it will help my leak):

https://bugzilla.redhat.com/show_bug.cgi?id=1400927

Even without doing the upgrade, I may need to restart glusterfs-server anyway to reset memory usage.

Thanks,

Jackie

On Dec 28, 2016, at 9:40 PM, Ravishankar N <ravishankar@xxxxxxxxxx> wrote:

On 12/29/2016 10:46 AM, Jackie Tung wrote:

Thanks very much for the advice.

Would you mind elaborating on the "no io" recommendation?  It's somewhat hard for me to guarantee this without a long maintenance window.

What is the consequence of having IO at point of add-brick, and for the heal period afterwards?

Sorry I wasn't clear. Since you're running  16 distribute legs (16x2), a lot of self-heals would be running and there is a chance that clients might experience slowness due to the self-heals. Other than that it should be fine.
Thanks,
Ravi

On Dec 28, 2016 8:27 PM, "Ravishankar N" <ravishankar@xxxxxxxxxx> wrote:

On 12/29/2016 07:30 AM, Jackie Tung wrote:

Version is 3.8.7 on Ubuntu xenial.

On Dec 28, 2016 5:56 PM, "Jackie Tung" <jackie@xxxxxxxx> wrote:

If someone has experience to share in this area, i'd be grateful.  I have an existing distributed replicated volume, 2x16.

We have a third server ready to go.  Redhat docs say just run add brick replica 3, then run rebalance.

The rebalance step feels a bit off to me.  Isn't some kind of heal operation in order rather than rebalance?

No additional usable space will be introduced, only replica count increase from 2 to 3.

You don't need to run re-balance for increasing the replica count. Heals should automatically be triggered when you run 'gluster vol add-brick <volname> replica 3 <list of bricks for the 3rd replica>`. It is advisable to do this when there is no I/O happening  on the volume. You can verify that files are getting populated in the newly added bricks post running the command.

-Ravi

Thanks

Jackie

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