Subject: Re: tuning TB RAID-backed filestore to reduce inode/superblock overhead
To: George Michaelson <>
From: Bill Studenmund <>
List: current-users
Date: 09/15/2004 17:30:57
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On Tue, Sep 07, 2004 at 07:50:09AM +0100, David Laight wrote:
> On Tue, Sep 07, 2004 at 11:36:38AM +1000, George Michaelson wrote:
> >=20
> > Is there a HOWTO for BSD which explains what is 'reasonable' overhead t=
o work=20
> > towards in constructing a 1.5Tb filestore on RAID?
> >=20
> > A co-worker just complained the consumed space for 1.5tb looked to be 1=
00Gb and
> > that seems a very high overhead. -no tunefs, no newfs options, no RAID =
tuning. Out
> > of the box.

What criteria did the co-worker use to get that 100 GB? Depending on what=
value s/he used, it might not be that far out of line. 100 GB / 1.5 TB =3D=
100 / (1.5 * 1024) =3D=3D 6.5%. We normally reserve 5% of the FS just for r=
(subtracted out of the "Avail" number reported in df), so 6.5% is really=20

> > Any simple guidance would be appreciated.
> The big overhead is the inodes, by default there is one inode for every
> 4 fragments (if not set by -i bytes-per-inode to newfs).
> With 1k fragments this is 1 inode for every 4k, FFSv1 inodes are 128
> bytes - so that is 1/32th of the disk space.  FFSv2 inodes are twice
> the size so will use 1/16th of the space.

Just for reference, that's 3.1% or 6.2% overhead for an inode

Take care,


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