Date: Sat, 20 Oct 2001 11:31:10 -0400 From: Brian T.Schellenberger <bts@babbleon.org> To: "Edward Gess" <edward_gess@hotmail.com>, freebsd-questions@FreeBSD.ORG Subject: Re: mysterious output of "df" utility... Message-ID: <01102011311000.05510@i8k.babbleon.org> In-Reply-To: <F240ZvYzPBpB7MsLuvj0000c1be@hotmail.com> References: <F240ZvYzPBpB7MsLuvj0000c1be@hotmail.com>
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Well, how much less is it?
It should be something like 8% less, since the "maximum" space per df is the
maximum user space, ignoring the space reserved for root only. Thus, if you
run (as root) a job like "cat /dev/zero > foo" and wait until it halts
because the entire partition is filled up, df will tell you that the
partition is 108% filled. (See the -m option under newfs.) This is what
accounts for the fact that Used + AVail < Size. And the Capacity is
calculated as
Used / Size * user-space-percentage ; normally that's Used / (0.92 * Size)
(Incidentally, Linux does exactly the same thing, although I believe it has a
somewhat smaller default reserved-space percentage.)
Another factor is that when it comes to disk space, sometimes "Meg" means
1,000 x 1000 = 1,000,000 and sometimes it means 1024 * 1024 = 1048576. This
set things off by another 5% or so; that is, if you allocate 1 decimal meg,
that's really only 0.952 binary meg.
If both of these factors are working against you, you could have about 13%
less space than you'd expect.
However, if the space is *grossly* smaller than what you think you allocated,
then something else is going on. For example, if you have less than half the
space you'd expect, perhaps you allocated n 512-byte sectors when meant to
allocate n K (1024 bytes).
On Saturday 20 October 2001 11:14, Edward Gess wrote:
> Hello,
> When I am using "df" utility to find out my disk usage info., I am
> getting stange output, i.e. the size is much smaller that should be!
> For example: during FreeBSD installation I gave for my root ("/") slice
> 50MB after installation with "df" utility I am getting that my root slice
> is < 50MB!!! Why??? More to that, when comparing "Used" and "Avail"
> fields,
> there much confusing thing! Logically the sum of "Used" and "Avail" must
> be
> equal to size of the slice, but it is much smaller than 50MB!!!
> If I would set "S" as a "Size" field of "df -h" output, "U" - "Used" and
> "A" - "Avail", so "S" is < than size of slice I've chosen during install.
> and "U" + "A" is < that "S", so I am loosing my free space!!! Please
> explain me
> this mysterious understanding of my space by "df" utility...
> Thanks.
>
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--
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Brian, the man from Babble-On . . . . bts@babbleon.org (personal)
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