07-11-2011
How sure are you that this will work? Truncating an open file is not guaranteed to release the space it uses, and the process(es) that already have the file open could very well just write more data at their current offset, which at best will create a sparse file.
The only way to make something like this work is if you have control of the application(s) generating the log file(s).
And if you have control of the application(s), you don't need a kludge like this because you'd have the app(s) properly manage their log files.
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vxiod(7) Miscellaneous Information Manual vxiod(7)
NAME
vxiod - Veritas Volume Manager I/O daemon process control device
DESCRIPTION
The vxiod device in Veritas Volume Manager (VxVM) is used to control the number of volume I/O daemons active on the system. A process con-
text is necessary to implement the plex consistency recovery and writeback error handling policies for multi-plex volumes, and for continu-
ing normal I/O after a log write if the volume has logging enabled. It is also required for the plex recovery performed with a mirrored
volume in the read/writeback mode.
There are three aspects of I/O daemon operations:
o General I/O
o Error handling
o Log handling
I/O handling is achieved by an ioctl command that does not return, but instead calls the vxiod routine to wait for errors or I/O requests
and process them. When an error occurs, if there are no I/O daemons active, the I/O simply turns into a failure on that plex. If a gen-
eral I/O request is queued up when no daemons exist, then the I/O will hang forever until a daemon process is created. If I/O daemons are
active, then the I/O is put on a work queue and the daemons are awakened. A daemon takes an error request and tries to read other plexes
until a read succeeds or all plexes have been tried. Then, if the writeback facility is enabled, the daemon tries to write the good data
to each plex that failed on the read. If the write is successful, the read error is nullified. An I/O request is handled in a similar
manner.
Logging is handled in a similar manner. An ioctl command, which does not return, is issued to create a daemon for each volume which has
logging enabled. This daemon monitors two queues: one queue of I/O which was started while the log was busy (the ``log'' queue), and
another queue of requests which have been logged and now need to be started (the ``ready'' queue). I/O requests are taken from the log
queue when the log is no longer busy, and another log write is started. Completion of a log write results in all I/O requests which have
just been logged being placed on the I/O daemon's ready queue where they are immediately started.
One mechanism finds out how many I/O error daemons are running, and another mechanism allows a process to become an I/O daemon. Before a
process becomes an I/O daemon, it should close all open files and detach from the controlling tty. An I/O or logging daemon cannot be
killed except through an explicit ioctl.
FILES
/dev/vx/iod vxiod control device
SEE ALSO
vxiod(1M), ioctl(2)
VxVM 5.0.31.1 24 Mar 2008 vxiod(7)