Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

VxFS Performance: Creating, Mounting, and Tuning File Systems
I/O Tuning
Chapter 248
hsm_write_
prealloc
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.
initial_extent_
size
Changes the default initial extent size. VxFS determines, based on
the first write to a new file, the size of the first extent to be allocated
to the file. Normally the first extent is the smallest power of 2 that is
larger than the size of the first write. If that power of 2 is less than
8K, the first extent allocated is 8K. After the initial extent, the file
system increases the size of subsequent extents (see
max_seqio_extent_size) with each allocation. Since most
applications write to files using a buffer size of 8K or less, the
increasing extents start doubling from a small initial extent.
initial_extent_size can change the default initial extent size
to be larger, so the doubling policy will start from a much larger
initial size and the file system will not allocate a set of small extents
at the start of file. Use this parameter only on file systems that will
have a very large average file size. On these file systems it will result
in fewer extents per file and less fragmentation.
initial_extent_size is measured in file system blocks.
max_buf_data_size The maximum buffer size allocated for file data; either 8K bytes or
64K bytes. Use the larger value for workloads where large
reads/writes are performed sequentially. Use the smaller value on
workloads where the I/O is random or is done in small chunks. 8K
bytes is the default value.