Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

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
57VxFS performance: creating, mounting, and tuning file systems
Tuning I/O