tune2fs -m "reserved space?"

[Justin Conover]

On 10/4/05, Arjan van de Ven <arjanv at redhat.com> wrote:
>
> On Tue, 2005-10-04 at 12:24 -0500, Justin Conover wrote:
> > tune2fs
> > -m reserved-blocks-percentage
> > -r reserved-blocks-count
> >
> > If what I have read is correct, -m by default uses 5% of the disk
> > space for "reserved root use" On my server at home with a /home of
> > 1TB thats about 50GB of wasted space.
> >
> > Is this reserved space actually used by ANYTHING? Like LVM, some kind
> > of fragmentation?
>
> well for emergency root stuff; logging in without any disk space is
> hard; lots of stuff wants to make temporary files etc.
>
> but your second point it true too: most filesystems (ext3 but most
> others) start to fragment like hell if they go over about 95% full.
>
> Think of it this way: if you have half your disk empty, the filesystem
> can do a proper job of finding non-fragmented space.
> If only 0.0001% is free, it has almost no freedom of choice, resulting
> in "you get it in whatever order some things become free".
> Those are sort of extremes; there's been a bunch of research and the
> outcome was that 5% free seems to be sort of the turning point in this
> respect.
>
> I suspect that research predates the Tb sized volumes, so I don't know
> if it maybe is 1% on such volumes, but then again to some extend the
> freedom needed will scale with the FS size
>
>
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>
> So, lets say you have a production server with a 20GB filesystem used for
a Oracle Database, would lowering it to 1-2% be safe or should you leave
this at default.

FYI, I'm not asking for support, just curious were the line is on
importance. You start getting in to 200GB-1TB file systems then you have a
pretty large area of un-allocated space.
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