HP-UX HB v13.00 Ch-14 - JFS

HP-UX Handbook – Rev 13.00 Page 22 (of 47)
Chapter 14 Journaled File System (JFS)
October 29, 2013
When the file stops being written, any unused space is freed for other files to use.
Normally 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. The default and minimum value of
max_seqio_extent_size is 2048.
default_indir_ size
On VxFS, files can have up to ten direct extents of variable size stored in the inode. After these
extents are used up, the file must use indirect extents which are a fixed size that is set when the
file first uses indirect extents.
These indirect extents are 8K by default. The file system does not use larger indirect extents
because it must fail a write and return ENOSPC if there are no extents available that are the
indirect extent size.
For file systems with many large files, the 8K indirect extent size is too small. The files that get
into indirect extents use many smaller extents instead of a few larger ones. By using this
parameter, the default indirect extent size can be increased so large that files in indirects use
fewer larger extents.
NOTE: The tunable default_indir_ size should be used carefully. If it is set too large, then
writes fail when they are unable to allocate extents of the indirect extent size to a file. In general,
the fewer and the larger the files on a file system, the larger the default_indir_ size can be set.
This parameter should generally be set to some multiple of the read_pref_io parameter.
default_indir_ size is not applicable on Version 4 disk layouts.
qio_cache_enable
Enables or disables caching on Quick I/O files. The default behavior is to disable caching. To
enable caching, set qio_cache_enable to 1. On systems with large memories, the database cannot
always use all of the memory as a cache.
By enabling file system caching as a second level cache, performance may be improved. If the
database is performing sequential scans of tables, the scans may run faster by enabling file
system caching so the file system performs aggressive read-ahead on the files.