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

Planning a Workgroup
Planning to Manage File Systems
Chapter 2100
The fscat utility provides an interface to a JFS snapshot file system,
similar to that provided by the dd utility invoked on the special file of
other JFS file systems. On most JFS file systems, the block or character
special file for the file system provides access to a raw image of the file
system for such purposes as backing up the file system to tape. The
fscat utility shows the snapshot as a stream of bytes that can be
processed in a pipeline or written to tape.
For more information, refer to fscat_vxfs (1M).
What size considerations does an administrator need to be aware of when
configuring a JFS file system?
Block size The recommended block size for JFS file systems is 1K.
Since JFS uses extents, there is no need to increase
this. However, if you decide to modify the block size,
you must recreate the file system. Use mkfs -F vxfs
-o bsize= n , where n is the block size in bytes and
represents the smallest amount of disk space that will
be allocated to a file. n must be a power of 2 selected
from the range 1024 to 8192; the default is 1024 bytes.
Disk space The only additional disk space used by JFS beyond
what is used by HFS is for the intent log. This averages
1 MB and cannot be greater than 2048 blocks.
Size of logical volume The maximum size allowed for a logical volume in
JFS is 4 GB.
Inodes JFS allocates inodes dynamically, without internal
restriction on the number possible, the sole restriction
being disk space. A JFS inode takes up 256 bytes. (JFS
inode creation differs from HFS, which has mkfs
allocate a fixed number of inodes in advance.)
In addition, JFS and HFS have the same limits for file and file-system
size:
• Maximum file size is 2 GB for HP-UX releases prior to 10.20, 128 GB
for HP-UX 10.20, or 1TB for HP-UX 11.x and thereafter.
• Maximum file-system size is 4GB for HP-UX releases prior to 10.20,
128 GB for HP-UX 10.20, or 1TB for HP-UX 11.x and thereafter.
What does JFS provide to ensure good performance?