SUMMARY: Where is the other 4GB?

From: Zu, Hongya <Zuh_at_pediatrics.ohio-state.edu>
Date: Mon, 15 May 2000 10:39:00 -0400

Original question:
Our Unix computer:
Model: Alpha Server 1200 5/533 DA-54KHC-DA
CPU: 533 MHz
Cache: 4 MB
RAM: 1256 MB
Hard Drive: 9.1 GB x 7 = 63.7 GB
Operating System: Digital Unix 4.0 E

The displays statistics on free disk space appears as below:
#> df -k
Filesystem 1024-blocks Used Available
Capacity Mounted on
        root_domain#root 262144 171421 71016
71% /
        usr_domain#usr 2097152 1913961 124608
94% /usr
        /dev/rz16c 51700393 47806362 0
103% /usr/users/data
/dev/re2c 4064238 1121350 2536464 31%
/usr/bioinfo
/dev/re1c 8620779 86 7758615
1% /usr/users/data/update
/proc 0 0 0
100% /proc

The disk mounted on /usr/users/data has almost 52GB. We used 48GB. Where is
the other 4GB?
Why is the Capacity 103%?
Answer:
* For each partition, there is a config. parameter which defines the maximum
use of it, often 90%
The Capacity measure is computed along with this parameter
51700393*90/100 = 46530353
47806362*100/46530353 = 102.74

so I get 103% !

*Don't forget overhead -i-nodes, directories, etc.

*don't know about advfs in particular, but read about the free space limit
in man newfs and man tunefs.
* m %free_space
The percentage of space reserved from normal users; the minimum free space
threshold (minfree). The default value is 10%. See tunefs(8) for more
details on how to set this option.
There is a fraction of disk space reserved and set aside. This is not
counted in the total, that's why your space can be greater than 100%,
because you are "eating" in this margin.
I guess today with large disk has no senso to use a 10% free space.

*It's a UFS file system. Part of the space may be wasted (depending on the
disk geometry), some of the space is used for file system metadata, and in a
UFS, a part of the space is normally reserved so that non-privileged users
can not fill the disk so full that the system can no longer do important
things like extend the size of a directory.

Thanks to:
Freesmeyer, Mary
Lucio Chiappetti
Dr. Tom Blinn
mc.vialatte_at_cust.univ-bpclermont.fr
Mitch Kulberg
N.M.Hill_at_rl.ac.uk
Gavin Kreuiter
Bochnik, William J
++++++++++++++++++++++++++++++++++++++++++
Hongya Zu, Ph.D
Research Information Service
Children's Research Institute
700 Children's Dr.
Columbus, OH 43205
Phone: (614)722-2914
Fax:(614)722-2716
++++++++++++++++++++++++++++++++++++++++++
Received on Mon May 15 2000 - 14:41:51 NZST

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