Filesystem mount options (HTFS, EAFS, AFS, S51K)
The Filesystem Manager supports the following mount options
for non-root HTFS, EAFS,
AFS, and S51K filesystems;
for root filesystems, see
``Modifying HTFS, EAFS, AFS, and S51K root filesystem mount configuration''.
Mount as Temporary Filesystem-
mounts the filesystem as a temporary data area (such as /tmp).
This improves system performance because the system updates
the information less frequently. (The potential for
loss of data is increased as a result.)
Checkpointing-
transitions the filesystem to a clean (consistent)
state at regular intervals. This reduces the probability that
your filesystem will need cleaning if the system is halted
unexpectedly.
Logging-
performs ``intent logging'', recording filesystem transactions
to a log file before they are
committed to disk. This increases data availability by reducing the
checking and repairing the filesystem to a few seconds.
This time is independent of filesystem size.
These options apply to HTFS filesystems only:
Maximum number of file versions-
determines maximum number of undeletable (versioned) files
allowed on the filesystem. A value of 0 disables versioning.
Minimum time before a file is versioned-
sets minimum time before a file is versioned. If set to 0, a file is
always versioned (as long as Maxiumum number of file versions
is greater than 0). If set to a value greater than 0, the file is versioned
after it has existed for that number of seconds.
See also:
Mounting as a temporary filesystem
To improve performance, your temporary filesystem (for example
/tmp, /u/tmp, or /usr/tmp), can be set up as
either an EAFS, AFS, S51K or
HTFS filesystem type. If you have any temporary
filesystems, you can select this option so
they are mounted as temporary filesystems automatically every time the
system is rebooted.
Temporary filesystems are updated less frequently and are
recommended for use on filesystems containing
temporary data only. If this option is used on /tmp, the overall
system performance may improve.
CAUTION:
Some applications use /tmp to save data.
If this option is enabled, then the
``checkpointing''
feature will be disabled automatically.
Checkpointing your filesystem
Checkpointing is the process of transitioning filesystems to a clean
(consistent) state. Filesystem data consists of user file data (the
contents of a file) and the data structures used to store the data
(also known as ``meta data''). Recently-accessed data is held
in memory (``cached'') for a short time in case it is needed again.
If the system is stopped unexpectedly, this cached data can be lost.
By default, HTFS, EAFS, AFS, and S51K
filesystems periodically
``checkpoint'' (write) cached meta data back to disk. This increases
the probability that the filesystem meta data will be in a consistent state
if the system is halted unexpectedly. (There may be a small loss of user data,
which is not checkpointed.)
If your system should experience a system error, checkpointing will
reduce the likelihood that the filesystem
will need to be checked and repaired with
fsck(ADM)
when rebooting, thus mimimizing downtime.
NOTE:
While checkpointing is appropriate for most users of HTFS,
there is a small performance penalty. To achieve maximum
throughput, you should consider disabling checkpointing.
See also:
Logging filesystem transactions
Intent logging minimizes system downtime after abnormal shutdowns
by logging filesystem transactions. When the system is halted
unexpectedly, this log can be replayed and outstanding transactions
completed. The check and repair time for filesystems can be reduced
to a few seconds, regardless of the filesystem size.
NOTE:
Intent logging does not increase the reliability of filesystem.
Only transactions concerning file meta data (the structures concerned
with storing data) are logged. The purpose is to
minimize system downtime.
The ability to locate and check only affected areas of the disk for
inconsistencies is central to the logging mechanism. The structure of the
mechanism is:
-
A log file is created as special file in the root of each mounted
filesystem. (This file is normally invisible and
is neither readable nor removable when logging is enabled.
When logging is disabled on a previously enabled filesystem, the
log file appears as .ilog0000.)
-
The location of the file is kept in the superblock (an area at the top
of the filesystem structure which describes the attributes of the
filesystem in terms of type, size, available space and latest modification
time).
-
Changes to a file's meta data (as opposed to the data it contains)
such as inodes
and block bitmaps are cached in memory. Before making any changes on disk,
a log entry is written synchronously. After the changes are
performed, a ``transaction complete'' indication is stored on disk.
If the system crashes before the log is written, it is as if the
change (any modifications to the filesystem) never occurred. If the system
crashes after the log is written, but before the transaction complete,
fsck either completes the change or undoes it.
If the system crashes after the transaction is completed, then the
modification has been completed, and there is nothing for fsck to do.
NOTE:
For optimum benefit, both logging and checkpointing
should be enabled. Checkpointing marks the filesystem as clean whenever
the filesystem is inactive. If the system needs to be checked (in the event
of an abnormal system halt, for instance) only areas of the disk
manipulated since the last checkpoint operation need to be
examined for inconsistencies.
See also:
Versioning filesystems (undelete)
Versioning allows deleted files to be recovered with the
undelete(C)
command or on the Desktop as described in
``Deleting and recovering files and directories''.
If versioning is enabled on a filesystem,
files and directories can be designated for versioning
and administered as described in
``Retrieving deleted files''.
The versioning feature can
be enabled system-wide or for individual filesystems.
To enable versioning on all non-root DTFS/HTFS
filesystems:
-
Use the Hardware/Kernel Manager as described in
``Configuration tools''.
Select category 10, ``Filesystem configuration.''
-
To enable
versioning
and set the maximum number (n) of versioned files,
set MAXVDEPTH to a non-zero number.
-
To disable versioning,
set MAXVDEPTH to 0
(default).
-
To set the number of seconds (n) before a file is
versioned,
set MINVTIME to n (a non-zero number).
The default value of MINVTIME is 0.
-
Relink the kernel with the new filesystem parameters -- see
``Relinking the kernel''.
-
Reboot the system by entering:
reboot
To enable versioning on a per-filesystem basis, see
``Filesystem mount options (HTFS, EAFS, AFS, S51K)''
and
``Filesystem mount options (DTFS)''.
To enable versioning on the root filesystem, see
``Modifying HTFS, EAFS, AFS, and S51K root filesystem mount configuration''
or
``Modifying HTFS, EAFS, AFS, and S51K root filesystem mount configuration''.
Next topic:
Filesystem mount options (DTFS)
Previous topic:
Enabling users to mount filesystems
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003