[linux-lvm] lvreduce thin-pool

Zdenek Kabelac zkabelac at redhat.com
Tue Jan 14 12:21:49 UTC 2020

Dne 14. 01. 20 v 10:52 Paul Dann napsal(a):
> Hi there,
> I've been following Ede Wolf's thread with interest, but it hasn't quite 
> covered my query, and I've not been able to find much about this in the archives:
> Are there any plans to implement reducing of thin pools? I've been bitten 
> several times by carelessly allowing a thin pool to expand onto unsuitable 
> storage and subsequently being unable to reduce the pool again to ensure IO 
> performance of the pool. (I know that better forward planning can mitigate this.)
> Mainly, I'm wondering if there are technical reasons this hasn't been 
> implemented yet? On the face of it, I'd have expected this to be a relatively 
> straight-forward procedure? But I'd be interested in why this might not be the 
> case.


There is no support for 'online' reduction of thin-pool. Mainly because there 
is not much interest into this.

For 'offline' reduction - you could probably write a tool working like this:

In kernel metadata figure out who holds the last 'chunk' and find what is the 
first 'empty' chunk - and copy the chunk there and remap all the references
to this last chunk to the new position.

Quite simple isn't  :) - the task would be probably simpler to code if it 
would be directly using thin tools from d-m-p-d package (i.e. thin_repair 

So basically a straight forward process, someone just needs to do all the 
coding for this.



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