The VxFS commands for manipulating extent attributes are setext and getext; they allow the user to set up files with a given
set of extent attributes or view any attributes that are already
associated with a file. See getext(1M) and setext(1M) for details on using these commands.
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 | NOTE: setext functionality is available only with the optional
HP OnLineJFS product. |
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The VxFS-specific commands vxdump and vxrestore, and the mv, cp, and cpio commands, preserve extent attributes when backing
up, restoring, moving, or copying files.
Most of these commands include a command line option (-e) for maintaining extent attributes on files. This
option specifies dealing with a VxFS file that has extent attribute
information including reserved space, a fixed extent size, and extent
alignment. The extent attribute information may be lost if the destination
file system does not support extent attributes, has a different
block size than the source file system, or lacks free extents appropriate
to satisfy the extent attribute requirements.
The -e option takes any of the following keywords as
an argument:
warn | Issues a warning message
if extent attribute information cannot be maintained (the default) |
force | Fails the copy if extent
attribute information cannot be maintained |
ignore | Ignores extent attribute
information entirely |
The commands that move, copy, or archive files (mv, cp and cpio) use the -e option with arguments of ignore, warn, or force.
For example, the mv command could be used with the -e option to produce the following results:
The ignore keyword loses any extent attributes for files.
The warn keyword issues a warning if extent attributes
for a file cannot be preserved. Such a situation may take place
if the file is moved into a non-VxFS file system; the file would
ultimately be moved while the extent attributes would be lost.
The force keyword issues an error if attributes are lost
and the file is not relocated.
The ls command has an -e option, which prints the extent attributes of
the file.
Failure to Preserve Extent Attributes |
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Whenever a file is copied, moved, or archived using commands
that preserve extent attributes, there is nevertheless the possibility
of losing the attributes. Such a failure might occur for three reasons:
The file system receiving a copied,
moved, or restored file from an archive is not a VxFS type. Since
other file system types do not support the extent attributes of
the VxFS file system, the attributes of the source file are lost
during the migration.
The file system receiving a copied, moved, or restored
file is a VxFS type but does not have enough free space to satisfy
the extent attributes. For example, consider a 50K file and a reservation
of 1 MB. If the target file system has 500K free, it could easily
hold the file but fail to satisfy the reservation.
The file system receiving a copied, moved, or restored
file from an archive is a VxFS type but the different block sizes
of the source and target file system make extent attributes impossible
to maintain. For example, consider a source file system of block
size 1024, a target file system of block size 4096, and a file that
has a fixed extent size of 3 blocks (3072 bytes). This fixed extent
size adapts to the source file system but cannot translate onto
the target file system.
The same source and target file systems in the preceding example
with a file carrying a fixed extent size of 4 could preserve the
attribute; a 4 block (4096 byte) extent on the source file system
would translate into a 1 block extent on the target.
On a system with mixed block sizes, a copy, move, or restoration operation
may or may not succeed in preserving attributes. It is recommended
that the same block size be used for all file systems on a given
system.
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