fcache_seqlimit_scope.5 (2010 09)

f
fcache_seqlimit_scope(5) fcache_seqlimit_scope(5)
(Tunable Kernel Parameters)
NAME
fcache_seqlimit_scope - sequential access detection control for file cache
VALUES
Failsafe
0
Default
0
Allowed values
The minimum value allowed is 0.
The maximum value allowed is 3.
DESCRIPTION
This parameter controls sequential access detection for different types of sequential accesses.
It is important to note the relationship between this tunable and
fcache_seqlimit_system
and
fcache_seqlimit_file
. These two tunables must be set to a value other than the default values. If
not, setting the tunable
fcache_seqlimit_scope
will not have any effect on the system. See
fcache_seqlimit_file(5) and fcache_seqlimit_system(5) for more information.
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 perfor-
mance degradation. In most cases, the default value should be sufficient.
This tunable has four settings:
fcache_seqlimit_scope = 0
This is the default setting. It corresponds to the HP-UX 11i v3 default behavior. Allows detec-
tion of all the sequential accesses.
fcache_seqlimit_scope = 1
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.
fcache_seqlimit_scope = 2
This setting allows detection of all the sequential writes.
fcache_seqlimit_scope = 3
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 writes.
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 performance 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
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1