Re: Where is the disk space?

[Marc MERLIN <marc@merlins.org>]

On Sat, Nov 14, 2015 at 10:35:39PM -0800, Liu Bo wrote:
> Since you said you have some snapshots in between...I can think of one
> case to prove where the space goes,
> 
> Say, you have a file with size=10M on a freshly created partition(the total used data space is 10M), and you have a snapshot which owns this file, then you modify the original file by overwrite the range [3M, 5M], and right now you can find that the total used data space increases to 15M or maybe more (because of unaliged write and extent pads to 4K length).
> 
> This comes from our COW and extent references implementation, so you get
> the benefit of COW, meanwhile have to live with the un-reclaimed space.
> 
> It's sort of something I was trying to fix, but I found that my approach
> led to other problems so I decided to give it up.

That's an interesting scenario. Thanks for explaining this.

MArc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901