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Solaris Tunable Parameters Reference Manual
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General File System Parameters

ncsize

Description

Defines the number of entries in the directory name look-up cache (DNLC). This parameter is used by UFS and NFS to cache elements of path names that have been resolved.

Starting with the Solaris 8 6/00 release, the DNLC also caches negative look-up information, which means it caches a name not found in the cache.

Data Type

Signed integer

Default

(4 x (v.v_proc + maxusers) + 320) + (4 x (v.v_proc + maxusers) + 320 / 100

Range

0 to MAXINT

Units

DNLC entries

Dynamic?

No

Validation

None. Larger values cause the time it takes to unmount a file system to increase as the cache must be flushed of entries for that file system during the unmount process.

When to Change

Prior to the Solaris 8 6/00 release, it was difficult to determine whether the cache was too small. You could make this inference by noting the number of entries returned by kstat -n ncstats. If the number seems high, given the system workload and file access pattern, this might be due to the size of the DNLC.

Starting with the Solaris 8 6/00 release, you can use the kstat -n dnlcstats command to determine when entries have been removed from the DNLC because it was too small. The sum of the pick_heuristic and the pick_last parameters represents otherwise valid entries that were reclaimed because the cache was too small.

Excessive values of ncsize have an immediate impact on the system because the system allocates a set of data structures for the DNLC based on the value of ncsize. A system running a 32-bit kernel allocates 36-byte structures for ncsize, while a system running a 64-bit kernel allocates 64-byte structures for ncsize. The value has a further effect on UFS and NFS, unless ufs_ninode and nfs:nrnode are explicitly set.

Commitment Level

Unstable

Change History

For information, see ncsize (Solaris 10 Release).

rstchown

Description

Indicates whether the POSIX semantics for the chown system call are in effect. POSIX semantics are as follows:

  • A process cannot change the owner of a file, unless it is running with UID 0.

  • A process cannot change the group ownership of a file to a group in which it is not currently a member, unless it is running as UID 0.

For more information, see chown(2).

Data Type

Signed integer

Default

1, indicating that POSIX semantics are used

Range

0 = POSIX semantics not in force or 1 = POSIX semantics used

Units

Toggle (on/off)

Dynamic?

Yes

Validation

None

When to Change

When POSIX semantics are not wanted. Note that turning off POSIX semantics opens the potential for various security holes. Doing so also opens the possibility of a user changing ownership of a file to another user and being unable to retrieve the file without intervention from the user or the system administrator.

Commitment Level

Obsolete

dnlc_dir_enable

Description

Enables large directory caching


Note - This parameter has no effect on NFS file systems.


Data Type

Unsigned integer

Default

1 (enabled)

Range

0 (disabled) or 1 (enabled)

Dynamic?

Yes, but do not change this tunable dynamically. You can enable this parameter if it was originally disabled. Or, you can disable this parameter if it was originally enabled. However, enabling, disabling, and then enabling this parameter might lead to stale directory caches.

Validation

No

When to Change

Directory caching has no known problems. However, if problems occur, then set dnlc_dir_enable to 0 to disable caching.

Commitment Level

Unstable

dnlc_dir_min_size

Description

Specifies the minimum number of entries cached for one directory.


Note - This parameter has no effect on NFS file systems.


Data Type

Unsigned integer

Default

40

Range

0 to MAXUINT (no maximum)

Units

Entries

Dynamic?

Yes, this parameter can be changed at any time.

Validation

None

When to Change

If performance problems occur with caching small directories, then increase dnlc_dir_min_size. Note that individual file systems might have their own range limits for caching directories. For instance, UFS limits directories to a minimum of ufs_min_dir_cache bytes (approximately 1024 entries), assuming 16 bytes per entry.

Commitment Level

Unstable

dnlc_dir_max_size

Description

Specifies the maximum number of entries cached for one directory.


Note - This parameter has no effect on NFS file systems.


Data Type

Unsigned integer

Default

MAXUINT (no maximum)

Range

0 to MAXUINT

Dynamic?

Yes, this parameter can be changed at any time.

Validation

None

When to Change

If performance problems occur with large directories, then decrease dnlc_dir_max_size.

Commitment Level

Unstable

segmap_percent

Description

Defines the maximum amount of memory that is used for the fast-access file system cache. This pool of memory is subtracted from the free memory list.

Data Type

Unsigned integer

Default

12 percent of free memory at system startup time

Range

2 Mbytes to 100 percent of physmem

Units

% of physical memory

Dynamic?

No

Validation

None

When to Change

If heavy file system activity is expected, and sufficient free memory is available, you should increase the value of this parameter.

Commitment Level

Unstable

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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire