[TUHS] tunefs -m 5%

[Warner Losh]

On Fri, Mar 5, 2021, 6:18 PM Greg 'groggy' Lehey <grog at lemis.com> wrote:

> On Friday,  5 March 2021 at 10:32:15 -0500, Theodore Ts'o wrote:
> > On Fri, Mar 05, 2021 at 01:50:32AM -0800, John Gilmore wrote:
> >> John P. Linderman <jpl.jpl at gmail.com> wrote:
> >>> I have several 12 TB disks scattered about my house. 5% of 12TB is
> 600GB.
> >>
> >> At one point in hystery, ext2 performance was reported to suffer badly
> >> if there was less than 5% of disk space available in an active
> >> filesystem.  My naive belief, probably informed by older and wiser heads
> >> around Sun, was that when the file system was >95% full, ext2 spent a
> >> lot of time seeking around in free lists finding single allocatable
> >> blocks.  And there were no built-in "defragmentation" programs that
> >> could easily fix that.
> >
> > I'll point out that BSD FFS, at least in BSD 4.3, reserves 10% of the
> > file system for reserved blocks.
>
> Oops, that's what I get for reading messages sequentially :-(  But in
> this case it's for small values of 10.
>

We set this to 1% at Netflix and fill to about ~98-99% full over UFS. This
works well as we don't have small files. SATA Flash we keep a bit more
empty, but that's due to its crappy FLT liking more free space...

Warner

Greg
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