Tuning the Number of Inodes and the Inode Hash Table

The Sun QFS file system enables you to set the following two tunable parameters in the /etc/system file:

• ninodes

• nhino

To enable non-default settings for these parameters, edit the /etc/system file, and then reboot your system.

ninodes Parameter

The ninodes parameter specifies the maximum number of default inodes. The value for ninodes determines the number of in-core inodes that Sun QFS software keeps allocated to itself even when applications are not using many inodes.

The format for this parameter in the /etc/system file is as follows:

set samfs:ninodes = _value_

The range for value is from 16 through 2000000. The default value for ninodes is one of the following:

• A value that is equal to the ncsize setting. The ncsize parameter is an Oracle Solaris tuning parameter that specifies the number of entries in the directory name look-up cache (DNLC). For more information about ncsize, see the Oracle Solaris Tunable Parameters Reference Manual.

• 2000. ninodes is set to 2000 if the ncsize setting is zero or out of range.

nhino Parameter

The nhino parameter specifies the size of the in-core inode hash table.

The format for this parameter in the /etc/system file is as follows:

set samfs:nhino = value

The range for value is 1 through 1048756. value must be a nonzero power of 2. The default value for nhino is one of the following:

• A value that is equal to the ninodes value divided by 8 and then, if necessary, rounded up to the nearest power of 2. For example, assume that the following line exists in /etc/system:

  set samfs:ninodes 8000

  For this example, if nhino is not set, the system assumes 1024, which is 8000 divided by 8 and then rounded up to the nearest power of 2 (210).

• nhino is set to 512 if the ninodes setting is out of range.

When to Set the ninodes and nhino Parameters

When searching for an inode by number, a Sun QFS file system searches its cache of in-core inodes. To speed this process, the file system maintains a hash table to decrease the number of inodes it must check.

A larger hash table reduces the number of comparisons and searches, at a modest cost in memory usage. If the nhino value is too large, the system is slower when undertaking operations that sweep through the entire inode list (inode syncs and unmounts). For sites that manipulate large numbers of files and sites that do extensive amounts of NFS I/O, setting these parameter values to larger than the defaults can be advantageous.

If your site has file systems that contain only a small number of files, consider making these numbers smaller than the defaults. For example, this setting might improve performance if you have a file system into which you write large single-file tar(1) files to back up other file systems.