bug#27162: [PATCH 0/6] Display how much will be downloaded

[Danny Milosavljevic]

Hi,

On Wed, 31 May 2017 12:42:29 -0700
Maxim Cournoyer <address@hidden> wrote:

> This is really neat! Thanks for that. Shouldn't the default behavior
> of build to stop right there (even without the -n flag) and errors out
> when it "knows" there won't be enough space to successfully build the
> derivations? 

It doesn't know it.

Modern filesystems can compress on-the-fly.  What free-disk-space shows is just 
a guess and it really depends on the exact content you write whether it will 
fit or not. 

Also, filesystems with deduplication will store content just once (basically at 
the sector with the number equal to the hash of the content) and just reuse the 
same sectors for other files.  That, too would be misjudged.

Then there are quotas, if there's a quota for a specific user only this user's 
files will be limited (much earlier).  Not supported either.

Then there can be storage reserved for the root user - and if you are non-root, 
you won't get it, even if it's technically "available".

Then there's clustering overhead.  Depending on the size of the individual 
files it can take (sometimes) much more space to actually store those files 
than you think.

Therefore I think a warning is better.  It can easily have both false positives 
and false negatives.

I like the feature, though.  Also the download size feature.  Nice :D