VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Chapter 14, Tuning for Performance
Prerelease 8 September 2005, 8:55am Tuning VxFS
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initial_extent_
size
Changes the default initial extent size. VxFS determines the size of the
first extent to be allocated to the file based on the first write to a new
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. The default value is 8K
bytes.
max_direct_iosz The maximum size of a direct I/O request that will be issued by the file
system. If a larger I/O request comes in, then it is broken up into
max_direct_iosz chunks. This parameter defines how much
memory an I/O request can lock at once, so it should not be set to more
than 20 percent of memory.
max_diskq Limits the maximum disk queue generated by a single file. When the
file system is flushing data for a file and the number of pages being
flushed exceeds max_diskq, processes will block until the amount of
data being flushed decreases. Although this doesn't limit the actual disk
queue, it prevents flushing processes from making the system
unresponsive. The default value is 1MB.