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

[Ludovic Courtès]

Danny Milosavljevic <address@hidden> skribis:

> 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.

All good points, indeed.

Ludo’.