[Dirvish] Too much disk space for images

Dave Howorth dhoworth at mrc-lmb.cam.ac.uk
Fri Oct 2 10:18:21 UTC 2009

Jenny Hopkins wrote:
> does this mean that the directory size of  20090712 is 0.2G PLUS the
> 31.7G from  20090705, then in turn the  20090719 is 1.8G PLUS the
> 31.7G PLUS the 0.2G?
> So that when image 20090705 is deleted, the du for 20090712 will show 31.9G?
> And so on down the line, so that if we deleted all images except
> 20090923, the final image, it still would be our 75.4GB?  (Apart from
> files that were overwritten by a larger size rather than added as
> new).

Not quite. You're basically right about the principle but you have to
remember that
(a) some files in the older snapshot have probably been deleted before
the newer snapshot. So you need to subtract them from the total to get
the true answer, and
(b) where a file has changed, there are then two copies. But there's
only one copy in each snapshot, so again you need to subtract the extra

I think if you ask du to tell you the size of just one particular
snapshot, it will give you a realistic answer for what would be left if
you deleted all the other snapshots. That's the easiest way to know the
size that I'm aware of.

Cheers, Dave

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