Re: [gentoo-user] {OT} rdiff-backup: push or pull?

[Alan McKinnon <alan.mckinnon@gmail.com>]

On Wed 17 August 2011 23:49:16 Alex Schuster did opine thusly:
> Grant writes:
> > >> > Can I reserve 0% for root on my USB hard drive which
> > >> > is only
> > >> > used for backups and does not contain an OS?
> > >> 
> > >> Yes:
> > >> 
> > >> mke2fs -m 0 /dev/usb-drive
> > > 
> > > Although a value > 0 helps against fragmentation. And when
> > > rdiff-backup has failed because it ran out of space,
> > > regressing to the previous sane state will need a little
> > > free space.> 
> > Good points.  Should 10GB (1% of 1TB) do it?
> 
> This I don't know. I use this value for large partitions of
> multimedia data, because I do not want to waste space (no matter
> how big the drives are, mine are always quite full), and
> performance should not be a big issue here. I keep the 5% default
> other partitions, like /home. BTW, you can also specify fractions
> like 0.5% if you like.

I prefer to keep reminding myself where 5% comes from. Way back when 
ext2 was being developed, 500M drives were big. 5% reserved is 12.5M 
or about 12,500 blocks.

Why that amount? Is it really 5% or is it the number of blocks and 5% 
just happens to round that out nicely?

Median file sizes haven't changed much in 15 years. The number of 
files on an average machine has increased hugely, and the upper size 
limit is orders of magnitude bigger, but that doesn't affect the 
median size much.

I take the view that 5% is excessive these days and usually reserve 
only a tiny amount - something like 10 x the biggest file I expect to 
have to deal with when the disk is full. 

And besides, as Murphy would have it, it's usually a root process that 
fills drives anyway (syslog cough cough) rendering the reserved amount 
useless :-)


-- 
alan dot mckinnon at gmail dot com