Ted Rodriguez-Bell wrote:
Has anyone done any testing to see what the right reserved block
percentage (-m to tune2fs or mke2fs) is? On the Berkeley Fast
Filesystem the right number was 10%; the ext2/ext3 default is 5% so I
assume that's pretty good for most Linux. But with so many layers
between Linux and the hardware, is that a good default on zSeries?
I ask because we've just noticed that Levanta left us with filesystems
where -m was 0. That gives us an interesting time with filesystem
monitoring (if you want an alarm at 90% of capacity, does it trigger
at 90% of the total blocks or 85.5%?), but we're also wondering if we
have any performance-related time bombs.
This is really not a question of the file system technology, but
merely depending on the use of the file system. The reserve is _not_
for any file system meta data but only for the root user. The system
is supposed to be able to write log files, and allow the root-user to
recover from the situation in case the file system runs full.
For file systems like /usr, a reserved blocks percentage of 0% is just
fine. Same for any data-disks that contain application data. For the
disks backing /root and /var, I'd recommend to leave some space
reserved there.
Also remember that the reserved percentage is relative to your file
system size. If you use many small file systems, you probably want
more reserved percentage then on a large one.
so long,
Carsten
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