[Gluster-users] rebalance on large filesystems

[Strahil]

On Oct 1, 2019 15:40, ML <lists at websiteburo.com> wrote:
>
> Hi there,
>
> I'm looking for the community's opinion on a gluster volume rebalance 
> I'm hestitating to start :)
>
> Here is my config :
>
> Volume Name: nas-3
> Type: Distributed-Replicate
> Status: Started
> Number of Bricks: 2 x 2 = 4
> Transport-type: tcp
> Bricks:
> Brick1: 192.168.0.1:/home/nas-3
> Brick2: 192.168.0.2:/home/nas-3
> Brick3: 192.168.0.3:/home/nas-3
> Brick4: 192.168.0.4:/home/nas-3
> Options Reconfigured:
> performance.quick-read: off
> performance.cache-size: 500MB
> performance.io-thread-count: 32
> transport.address-family: inet
> performance.readdir-ahead: on
>
> The bricks are constitued of 4 gluster servers version 3.10.12 :
>
> 192.168.0.1 + 192.168.0.2 = 2 x 22 TiB (global usage : 86%)
> 192.168.0.3 + 192.168.0.4 = 2 x 7   TiB (global usage : 40%) (this 2 
> bricks came 1 year after the 2 first ones, without rebalance after went 
> live)
>
> Actual usage :
>
> on 192.168.0.1 + 192.168.0.2 : /home/nas-3 = 2 x 14,5TiB (Items: 49327658)
> on 192.168.0.3 + 192.168.0.4 : /home/nas-3 = 2 x 2,8TiB (Items: 10343981)
>
> I need advice regarding :
>
> - Should I rebalance to fill the 2 x 7.2TiB servers ? (I need space on 
> the 22TiB servers)

I would say - yes.

> - Is rebalance process dividing files based on disk usage for each 
> connected brick ? (I'm afraid to see my 7.2 TiB servers become full)
Nah... Gluster is way smarter than that.Still, distribution is calculated via an algorithm which we can easily call hashing.Each brick has a hash range and when a file is not on it's hashed location - you should rebalance.

By the way, this should have been done when you added the new bricks.

For details, check: https://staged-gluster-docs.readthedocs.io/en/release3.7.0beta1/Features/dht/


> - Given the number of files stored, how to get an idea of the time 
> needed for the rebalance process to be complete ?

You can't estimate that with high accuracy as you got plenty of variables ->  number of files that should be balanced,size of the files that should be balanced, network bandwidth, load on the volume from your clients, speed  of the underlying disks, etc.

It could take a week , maybe less .

> Thank you for reading me & considering answering :))
>
> (If there's a gluster consultant you would recommand for these 
> questions, please let me know)
>
> Quentin
>
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Best Regards,
Strahil Nikolov
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