and
/etc/lvmtab_p
, which means that data of a logical volume might not be evenly distributed
over all the physical volumes within your volume group.
As a result, when I/O access to the logical volumes occurs, one or more disks within the volume
group might be heavily used, while the others might be lightly used, or not used at all. This
arrangement does not provide optimum I/O performance.
As a better alternative, you can set up your logical volume on specific disks in an interleaved
manner, thus balancing the I/O access and optimizing performance (see
“Extending a Logical
Volume” (page 53)
).
Because there are no HP-UX commands that identify that the contents of a logical volume are being
used for raw data, use recognizable names for the logical volumes you create for raw data. In
this way, you can recognize the contents of such a logical volume.
Setting Up Logical Volumes for File Systems
File systems reside in a logical volume just as they do within disk partitions or nonpartitioned disks.
Two types of file systems can be used in a logical volume: Hierarchical File Systems (HFS) and
Journaled File Systems (JFS) (VxFS).
Choosing the Initial Size of File System Logical Volumes
When determining the required space for a file system, consider the three major components shown
in
Figure 3
.
Figure 3 File System Space Components
To estimate how big to make a logical volume that will contain your file system, follow these steps:
1.
Estimate how much disk space users will need for their data in the future. Allow for any
anticipated changes, which usually include additional growth. (Use the
du
command to see
how much disk space is currently used.)
2.
Add 10% to the above amount for a “minfree” area; this area is reserved to maintain
performance.
3.
Add another 5% for file system overhead; this includes all data structures required to maintain
the file system.
4.
Round up to the next integer multiple of the logical extent size used in this logical volume to
find the size in logical extents. (This step is performed automatically when you create a logical
volume.)
For example, if a group of users will require 60 MB space for file system data, the following
estimate allows for expected growth. Add 6 MB for the minfree space. Then add 3 MB for file
system overhead for a total estimate of 69 MB required by the file system, and 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 4 MB, round 69 to 72 to make it divisible by 4 MB.
Although these estimates are not precise, they suffice for planning a file system size. Create your
file system large enough to be useful for some time before increasing its size.
Setting Up Different Types of Logical Volumes
21
