Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Administering a System: Managing Disks and Files
Managing Disks
Chapter 6564
For example, suppose a group of users will require 60MB space for file
system data; this estimate allows for expected growth. You then add
6MB for the “minfree” space and arrive at 66MB. Then you add another
3MB for file system overhead and arrive at a grand total estimate of
69MB required by the file system, and by consequence, for the logical
volume that contains the file system. If you are creating the logical
volume in a volume group that has an extent size of 4MB, 69 gets
rounded up to 72 to make it divisible by 4MB. That is, LVM will create
your logical volumes in multiples of the logical extent size.
Although estimates are not precise, they suffice for planning how big to
make a file system. You want your file system to be large enough for
some useful time before having to increase its size. On the other hand, a
contiguous logical volume such as the root logical volume cannot be
readily increased in size. Here, it is especially important to try to choose
an estimate that will allow for all subsequent growth to such logical
volumes.
Suppose as suggested above, your users have outgrown the space
originally allocated for the file system. You can increase the size of a file
system by first enlarging the logical volume it resides in and then using
extendfs (1M). (More information can be found under “Extending the Size
of a File System Within a Logical Volume” on page 611).
You cannot decrease the size of a file system once it has been created.
However, you can create a new smaller file system to take its place.
NOTE Because increasing the size of a file system is usually much easier than
reducing its size, you might benefit by being conservative in estimating
how large to create a file system.
However, an exception to this would be the root file system since it is
difficult to extend it.
Whenever possible, if you plan to have a file system span disks, have the
logical volume span identical disk interface types. (See “Using Disk I/O
Interfaces” on page 567.)
Normally, by default, LVM will create logical volumes on available disks,
not necessarily with regard for best performance. It is possible to have a
file system span two disks with different characteristics, in which case
the file system performance could possibly be impaired.