Summary: df -k : discrepancy in the % displayed
From: Ramesh Pathak (ramesh.pathak_at_vinciti.com)
Date: 08/28/03
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To: <sunmanagers@sunmanagers.org> Date: Thu, 28 Aug 2003 05:03:46 +0530
Let me thank all the great guys who responded to my query so fast.
Here are the excerpts from the mails that I received.
The reason is "minfree" taking some bytes out from the user.
And Paul also suggests that fragmentation may add to it further.
Thanks to all of you,
Ramesh
Michael Schulte
===========
The standard file system reserves about 10% of the kbytes for efficiency; it
is unavailable to anyone except root. Notice that the used+avail !=
kbytes.
VAleriy
========
If you created your filesystem with default options, 10% of the space
was reserved for root only access. So, in reality, you have to divide it
by (0.9*963869), i.e.
963869kb available total, take 10% for root only writes and you'll get
867462.1, now 185680/867462.1 = 21%
see man newfs section for -m option
Tom Payerle
=========
On Unix filesystems, there is typically some portion of a filesystem which
is reserved for root only; i.e. once a filesystem is filled to a certain
point,
only root can write to it. This is useful for stuff like / and /usr to
enable
things to work pretty well even when filesystems get "full". I think the
mkfs/newfs commands default to about 5% for this root reservation. Some
systems (I forget whether Solaris has this) have tunefs type commands that
can alter it once the filesystem is up and running, others it must be done
at creation time.
In your root case,
used (185680) + avail (720357) = 906037 or 57832 less than in kbytes field.
(which is 6% of the total).
Note that 185680/906037 = 20.5%
This 5% or so reservation is probably not worth bothering with on a 1-2GB
system disk or partitions (/, /usr, /var, etc). It probably is worth messing
with when dealing with 10 GB or more data only partitions (e.g. the system
can function pretty well if partition was missing), although to be honest
even in those cases I usually haven't done anything about it.
Tom Payerle
Dept of Physics payerle@physics.umd.edu
University of Maryland (301) 405-6973
College Park, MD 20742-4111 Fax: (301) 314-9525
ID16314 Explanation of file system usage as reported by df and fsck
Paul Richards
==============
:df output
: Filesystem kbytes used avail capacity ...
:/dev/sd2d 1961966 1745945 19825 99% ...
:1961966 kbytesFile system size
:1745945kbytes usedAmount used
:19825 kbytes freeEqual to (size less minfree%) less used
:99%Equal to used as % of (size less minfree%)
so minfree can affect the answer
also fragmentation can have an effect
:For example, in a file system that creates predominantly 5k files on an
:8k block size there will be many 3k frags free and never used. In the
:extreme case this would result in a file system that is effectively
:full despite only 5/8 of the filesystem being used.
Jay Lessert
========
minfree.
Looks like / was built with 6% minfree and /usr with 2% minfree.
/: 185680/(0.94 * 963869) = 20.5%
/: 2263070/(0.98 * 3099093) = 74.51%
You can see current minfree (and lots of other interesting information
about a file system with:
% sudo fstyp -v /dev/rdsk/c0t0d0s0
Crist J. Clark
========
Read df(1),
-k Print the allocation in kbytes. The output consists of
one line of information for each specified file sys-
tem. This information includes the file system name,
the total space allocated in the file system, the
amount of space allocated to existing files, the total
amount of space available for the creation of new
files by unpriviledged users, and the percentage of
^^^^^^^^^^^^^
normally available space that is currently allocated
to all files on the file system. This option overrides
the -b, -e, -n, and -t options.
And newfs(1M),
-m free
The minimum percentage of free space to maintain
in the file system (between 1% and 99%,
inclusively). This space is off-limits to normal
users. Once the file system is filled to this
threshold, only the super-user can continue
writing to the file system. This parameter can
be subsequently changed using the tunefs(1M)
command.
The default is ((64 Mbytes/partition size) *
100), rounded down to the nearest integer and
limited between 1% and 10%, inclusively.
Lars
====
man newfs(1m), -m option.
capacity = used / ( used + avail )
used + avail < kbytes.
--
Omnibiblious, adj.:
Indifferent to type of drink. "Oh, you can get me anything.
I'm omnibiblious."
Eugene
=========
Hi
By default a certain amount of space is allocated as "reserved for root use
only". This space is also commonly referred to as "slosh space".
This can be modified with tunefs (see man page).
The calculation takes this into account. Typically this is between 1 and 10
%, depending on the FS size.
-----Original Message-----
The % available is based on the 90% level of capacity:
/: ( 185680 / (.90 * 963869)) = 21%
Mark
==========
thats because when you do a defualt newfs it save 10% for superuser.. man
newfs and look for the -m option:
-m free The minimum percentage of free space to
maintain in the file system. This space
is off-limits to normal users. Once the
file system is filled to this threshold,
only the super-user can continue writing
to the file system. This parameter can
be subsequently changed using the
tunefs(1M) command. The default is 10%.
So with a newfs -m 3 /dev/dsk/c0t0d0s0 will give you 7% more disk space
for that partition...
Hope this helps...
Kevin
=====
The capacity percentage reported by "df -k" is the amount of user
writable space that is in use. What you're calculating is the total
amount of space that is in use. By default, UFS filesystems reserve 10%
of the space in the filesystem that can only be written to by root (as an
aside, this can and should be changed when large filesystems are created;
10% of a 1 TB filesystem is a lot of wasted space). This is also why you
can see filesystems that are more than 100% full. HTH...
==================================
Kevin Buterbaugh - Systems Engineer
LifeWay - www.lifeway.com
Man tunefs
Look at the -m Option and it was clearer ;-)
--
Michael Schneider MM-ITconsulting
Sun Certified Network Administrator Ph: +49(0)700
Ramesh C Pathak
Vinciti Networks Pvt. Ltd.,
#1109, 24th Main Road,
JP Nagar 1st Phase,
Bangalore - 560 078
Ph: +91-80-6556830
Fax: +91-80-6556820
email: ramesh.pathak@vinciti.com
URL: http://www.vinciti.com
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