Veritas™ File System 5.0.1 Administrator's Guide

Table 2-1
Tunable VxFS I/O parameters (continued)
DescriptionParameter
Specifies the time, in seconds, that must elapse before the
VxFS File Change Log (FCL) records a data overwrite, data
extending write, or data truncate for a file. The ability to
limit the number of repetitive FCL records for continuous
writes to the same file is important for file system
performance and for applications processing the FCL.
fcl_winterval is best set to an interval less than the
shortest interval between reads of the FCL by any
application. This way all applications using the FCL can
be assured of finding at least one FCL record for any file
experiencing continuous data changes.
fcl_winterval is enforced for all files in the file system.
Each file maintains its own time stamps, and the elapsed
time between FCL records is per file. This elapsed time
can be overridden using the VxFS FCL sync public API.
See the vxfs_fcl_sync(3) manual page.
fcl_winterval does not apply to disk layout Versions
1 through 5.
fcl_winterval
For a file managed by a hierarchical storage management
(HSM) application, hsm_write_prealloc preallocates disk
blocks before data is migrated back into the file system.
An HSM application usually migrates the data back
through a series of writes to the file, each of which
allocates a few blocks. By setting hsm_write_ prealloc
(hsm_write_ prealloc=1), a sufficient number of disk
blocks are allocated on the first write to the empty file so
that no disk block allocation is required for subsequent
writes. This improves the write performance during
migration.
The hsm_write_ prealloc parameter is implemented
outside of the DMAPI specification, and its usage has
limitations depending on how the space within an
HSM-controlled file is managed. It is advisable to use
hsm_write_ prealloc only when recommended by the
HSM application controlling the file system.
hsm_write_ prealloc
55VxFS performance: creating, mounting, and tuning file systems
Tuning I/O