AIX 5L Problem Determination - IBM Redbooks

In many cases, restoration of the backup of the superblock to the primary
superblock will recover the file system. If this does not resolve the problem,
recreate the file system and restore the data from a backup.
7.4.4 Sparse file allocation
Some applications, particularly databases, maintain data in sparse files. Files
that do not have disk blocks allocated for each logical block are called sparse
files. If the file offsets are greater than 4 MB, then a large disk block of 128 KB is
allocated. Applications using sparse files larger than 4 MB may require more disk
blocks in a file system enabled for large files than in a regular file system.
In the case of sparse files, the output of the ls command is not showing the
actual file size, but is reporting the number of bytes between the first and last
blocks allocated to the file, as shown in the following example:
# ls -l /tmp/sparsefile
-rw-r--r-- 1 root system 100000000 Jul 16 20:57 /tmp/sparsefile
The du command can be used to see the actual allocation, since it reports the
blocks actually allocated and in use by the file. Use du -rs to report the number
of allocated blocks on disk.
# du -rs /tmp/sparsefile
256 /tmp/sparsefile
Note: The tar command does not preserve the sparse nature of any file that
is sparsely allocated. Any file that was originally sparse before the restoration
will have all space allocated within the file system for the size of the file. New
AIX 5L options for the backup and restore command are useful for sparse
files.
Using the dd command in combination with your own backup script will solve this
problem.
7.4.5 Unmount problems
A file system cannot be unmounted if any references are still active within that file
system. The following error message will be displayed:
Device busy
or
A device is already mounted or cannot be unmounted
154 IBM ^ Certification Study Guide - AIX 5L Problem Determination Tools and Techniques