fcache_seqlimit_scope(5)fcache_seqlimit_scope(5)NAMEfcache_seqlimit_scope - sequential access detection control for file
The minimum value allowed is
The maximum value allowed is
This parameter controls sequential access detection for different types
of sequential accesses.
It is important to note the relationship between this tunable and and
These two tunables must be set to a value other than the default val‐
ues. If not, setting the tunable will not have any effect on the sys‐
tem. See fcache_seqlimit_file(5) and fcache_seqlimit_system(5) for
Customers must consider the file system sequential operations in their
workload environment before changing the value of this tunable from the
default value on production systems. It is specifically used to
improving sequential I/O performance for large files. Setting an
improper value may cause system performance degradation. In most
cases, the default value should be sufficient.
This tunable has four settings:
This is the default setting. It corresponds to the HP-UX 11i v3
default behavior. Allows detection of all the sequential
This setting allows detection of all the sequential reads.
It is appropriate to set this value if file system is
doing more sequential reads to a large file than writes.
This setting allows detection of all the sequential writes.
This setting allows detection of sequential append only writes.
Who is Expected to Change This Tunable?
System administrators that run applications which do large sequential
file I/O's. Typically, these files are larger than the size of the
file cache on the system.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Value of This Tunable Be Changed to 1?
This tunable should be changed from 0 to 1 if applications are expected
to do more sequential reads than writes.
When Should the Value of This Tunable Be Changed to 2?
This tunable should be changed to 2 if applications are expected to do
more sequential writes to a large file than reads.
When Should the Value of This Tunable Be Changed to 3?
This tunable should be changed to 3 if applications are expected to do
more sequential append only writes than sequential reads and non-append
What Are the Side Effects of Changing the Value?
Setting the tunable other than the default value may cause more page
outs. Setting the tunable to an improper value may yield poor perfor‐
mance for large sequential I/O's on large files (larger than physical
memory size). For example if an application is doing more sequential
writes than reads, setting the tunable to a value other than 2 will
cause system performance degradation.
The tunable should be exercised with extreme caution as it will have
impact on file system throughput.
What Other Tunable Values Should Be Changed at the Same Time?
and should be changed to other than the default value.
All HP-UX kernel tunable parameters are release specific. This parame‐
ter may be removed or have its meaning changed in future releases of
Installation of optional kernel software, from HP or other vendors, may
cause changes to tunable parameter values. After installation, some
tunable parameters may no longer be at the default or recommended val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
was developed by HP.
SEE ALSOfcache_seqlimit_file(5), fcache_seqlimit_system(5).
Tunable Kernel Parameters fcache_seqlimit_scope(5)