SUMMARY: how to lowering FS reserved space?

From: Daniel Vega Villa (daniel.vega@yucatan.gob.mx)
Date: Thu Jan 18 2007 - 18:54:17 EST

Thanks to Terry Franklin who promptly responded straigth to the solution:

tunefs (1M) can help reducing the 10% default value, but I found in man pages
that there are some considerations to take before any movement, that I will
share:

>From docs.sun.com:
"
     -m minfree
This value can be set to 0; however, up to a factor of three in throughput
will be lost over the performance obtained at a 10% threshold. Note: If the
value is raised above the current usage level, users will be unable to
allocate files until enough files have been deleted to get under the higher
threshold.
"

And from http://leaf.dragonflybsd.org/cgi/web-man?command=tunefs&section=8 :

     -m minfree
             .... Settings of 5% and less force space optimization to
             always be used which will greatly increase the overhead for file
             writes. ....
     -o space | time
             The filesystem can either try to minimize the time spent allocat-
             ing blocks, or it can attempt to minimize the space fragmentation
             on the disk. Optimization for space has much higher overhead for
             file writes. The kernel normally changes the preference automat-
             ically as the percent fragmentation changes on the filesystem.

So I will leave the minfree default 10% for performance reasons.

Thanks a lot.

Daniel.
________________________________________
De: terry.franklin@gmail.com [mailto:terry.franklin@gmail.com] En nombre de
Terry Franklin
Enviado el: Jueves, 18 de Enero de 2007 05:35 p.m.
Para: Daniel Vega Villa
Asunto: Re: how to lowering FS reserved space?

Are you looking for tunefs? tunefs -m <minfree> will adjust what you are
referring to. See tunefs(1M) for more info.

Terry
On 1/18/07, Daniel Vega Villa <daniel.vega@yucatan.gob.mx> wrote:
Hi fellow admins,

I've been searching (without any luck) for the steps how to lower the
reserved space of the file systems, here is an example:

Filesystem size used avail capacity Mounted on
/dev/md/dsk/d0 9.6G 7.2G 2.3G 76% /
/dev/vx/dsk/datadg/voldb1 64G 51G 6.8G 89% /db1
/dev/vx/dsk/datadg/voldb4 32G 26G 2.5G 92% /db4
/dev/vx/dsk/datadg/voldb2 128G 114G 1.7G 99% /db2
/dev/vx/dsk/datadg/voldb5 64G 18G 40G 32% /db5
/dev/vx/dsk/datadg/voldb3 64G 51G 6.9G 88% /db3
...
..

As you may see, the numbers doesn't correspond if you do the math!,
taking as anexample db3
size = 64G (100%)
used = 51G ( 79% real but listed 88%)
avail = 6.9G (11% aprox.)

I know that the 10% "lost" is for integrity info, but it's a lot!!
No matter it's a Veritas VM volume, SVM volume or a single slice volume
it reserves the 10%!
Uname -a output:
SunOS srvdb 5.9 Generic_118558-25 sun4u sparc SUNW,Sun-Fire-880

How can I lower this value of 10%?

Thanks in advance,
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