HP-UX Reference (11i v1 00/12) - 1M System Administration Commands N-Z (vol 4)

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man1m/naaagt.1m
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v
vxtunefs(1M) vxtunefs(1M)
of the read_pref_io parameter.
This tuneable does not apply to disk layout Version 4.
discovered_direct_iosz
Any file I/O requests larger than the discovered_direct_iosz are handled as discovered
direct I/O. A discovered direct I/O is unbuffered like direct I/O, but it does not require a synchronous
commit of the inode when the file is extended or blocks are allocated. For larger I/O requests, the
CPU time for copying the data into the buffer cache and the cost of using memory to buffer the I/O
becomes more expensive than the cost of doing the disk I/O. For these I/O requests, using discovered
direct I/O is more efficient than regular I/O. The default value of this parameter is 256K.
initial_extent_size
Changes the default size of the initial extent.
VxFS determines, based on the first write to a new file, the size of the first extent to allocate to the
file. Typically 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.
Because 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
changes the default initial extent
size to a larger value, so the doubling policy starts from a much larger initial size, and the file system
won’t allocate a set of small extents at the start of file.
Use this parameter only on file systems that have a very large average file size. On such file systems,
there are fewer extents per file and less fragmentation.
initial_extent_size
is measured in file system blocks.
max_buf_data_size
Determines the maximum buffer size allocated for file data. The two accepted values are 8K bytes
and 64K bytes. The larger value can be beneficial for workloads where large reads/writes are per-
formed sequentially. The smaller value is preferable on workloads where the I/O is random or is done
in small chunks. The default value is 8K bytes.
max_direct_iosz
Maximum size of a direct I/O request issued by the file system. If there is a larger I/O request, it is
broken up into max_direct_iosz
chunks. This parameter defines how much memory an I/O
request can lock at once; do not set it to more than 20% 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 block until the amount of
data being flushed decreases. Although this does not limit the actual disk queue, it prevents syn-
chronizing processes from making the system unresponsive. The default value is 1 megabyte.
max_seqio_extent_size
Increases or decreases the maximum size of an extent. When the file system is following its default
allocation policy for sequential writes to a file, it allocates an initial extent that is large enough for the
first write to the file. When additional extents are allocated, they are progressively larger (the algo-
rithm tries to double the size of the file with each new extent), so each extent can hold several writes
worth of data. This reduces the total number of extents in anticipation of continued sequential writes.
When there are no more writes to the file, unused space is freed for other files to use.
In general, this allocation stops increasing the size of extents at 2048 blocks, which prevents one file
from holding too much unused space.
max_seqio_extent_size is measured in file system blocks.
read_nstream
The number of parallel read requests of size read_pref_io to have outstanding at one time. The
file system uses the product of read_nstream and read_pref_io to determine its read ahead
size. The default value for read_nstream is 1.
read_pref_io
The preferred read request size. The file system uses this in conjunction with the read_nstream
value to determine how much data to read ahead. The default value is 64K.
Section 1M−−1058 − 2 − HP-UX Release 11i: December 2000
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