sys_attrs_vfs(5)						File Formats Manual						  sys_attrs_vfs(5)

NAME

       sys_attrs_vfs - system attributes for the vfs kernel subsystem

DESCRIPTION

       This reference page describes system attributes for the Virtual File System (vfs) kernel subsystem.

       Do  not	directly  edit	the  system  configuration  file  to   change  a  system  attribute  value; use the dxkerneltuner application, the
       /sbin/sysconfig -r command, or the sysconfigdb command. See dxkerneltuner(8), sysconfig(8), and sysconfigdb(8) for more	information  about
       your options for configuring kernel subsystems.

       Some  subsystem attributes can be changed at run time. If so, the attribute descriptions in the following subsections mention that fact. To
       make it easy for you to locate these attributes when scanning lists, an asterisk (*) also precedes the names of these attributes.

   vfs Subsystem Attributes
	      Percentage of memory that the kernel wires for the metadata buffer cache.

	      Default value: 3 (percent) for 32-MB or larger systems; 2 (percent) for 24-MB systems

	      Minimum value: 0

	      Maximum value: 50

	      Increasing the value of the bufcache attribute can improve I/O performance by providing more memory  for	caching  UFS  file  system
	      data.  Decreasing the value of the bufcache attribute can free memory resources. For systems that cache only AdvFS file system data,
	      you may want to decrease the value to 1.

	      Size, in slots, of the hash chain table for the metadata buffer cache. The hash chain table is used to store the heads of the hashed
	      buffer queues.

	      Default value: 2048 (slots)

	      Minimum value: 0

	      Maximum value: 524,287

	      A  large hash chain table distributes the buffers and may make chain lengths short.  Increasing the size of the hash chain table can
	      reduce linear searches and improve lookup speed.

	      The number of pages to reserve for UBC buffers.

	      Default value: Calculated from the value of the bufcache attribute and system memory size.

	      Minimum value: 0

	      Maximum value: Varies, depending on how much memory the system has.

	      The value of bufpages overrides the value of bufcache, which sets the size of the metadata buffer cache as a percentage of available
	      memory  (in  whole numbers only) rather as a specific number of pages. Normally, sizing the metadata buffer cache in terms of a per-
	      centage rather than page count is appropriate. However, if you want the size of this buffer cache to be between 0 and 1  percent	of
	      available  memory,  you must set the bufpages value to the number of pages equal to that percentage. This sort of setting is extreme
	      and only feasible on very large memory (VLM) systems.

	      A value that enables (1) or disables (0) the pipe code that attempts to do batch writes to a pipe and deliver the data in  a  single
	      call to a reader.

	      Default value: 1 (enabled)

	      A value that determines whether maximizing UFS I/O throughput to keep a device busy (within the constraints of the io_throttle_shift
	      attribute) is enabled (1) or disabled (0). If io_throttle_maxmzthruput is disabled, the availability of dirty  pages  is	maximized,
	      which enables the operating system to decrease the time spent waiting for dirty pages.

	      You  may	want to consider disabling io_throttle_maxmzthruput if your I/O is limited to a small number of I/O-intensive applications
	      that access a specific set of pages.  In this case, maximizing the availability of dirty pages is more important	than  keeping  the
	      I/O  device  busy.   In  addition, if you have an environment that cannot tolerate delays in accessing sets of frequently-used dirty
	      pages, you may want to consider disabling io_throttle_maxmzthruput.

	      Default value: 1 (enabled)

	      You can modify this attribute at run time.

	      A value that limits the maximum number of concurrent delayed UFS I/O requests on an I/O device queue. The more requests on a  device
	      queue,  the  more time is required to process those requests and make those pages and the device available. The number of concurrent
	      delayed I/O requests on an I/O device queue can be limited by setting the io_throttle_shift attribute. The throttle value  is  based
	      on this attribute and the calculated I/O completion rate. The throttle value is proportional to the time required to process the I/O
	      device queue.

	      The relation between the value of the io_throttle_shift attribute and the time it takes to process the device queue is shown in  the
	      following table.

	      -----------------------------------------------------------------
	      Value of io_throttle_shift   Time  to  Process  Device  Queue in
					   Seconds
	      -----------------------------------------------------------------
	      -4			   .0625
	      -3			   .125
	      -2			   .25
	      -1			   .50
	      0 			   1
	      1 			   2
	      2 			   4
	      3 			   8
	      4 			   16
	      -----------------------------------------------------------------

	      For example, if io_throttle_shift is 0 (zero), the queue of UFS I/O requests requires approximately 1 second to process.	  Environ-
	      ments  that  cannot  tolerate  delays  in  accessing a device queue may want to consider reducing the default value of the io_throt-
	      tle_shift attribute.

	      Default value: 1

	      Minimum value: -4

	      Maximum value: 4

	      You can modify this attribute at run time.

	      A static limit on the number of asynchronous UFS I/O requests that can be put on the device queue. The default value  of	 0  (zero)
	      allows the operating system to determine the optimal rate.

	      Default value: 0

	      Minimum value: 0

	      Maximum value: 4,294,967,295

	      You can modify this attribute at run time.

	      Obsolete attribute. The operating system no longer uses this value.

	      Maximum  number  of UFS or MFS file system mounts.  You can increase the	value of the max_ufs_mounts attribute if you want to mount
	      more than the default number of UFS or MFS file systems. This attribute does not affect performance.

	      Default value: 1000 (file system mounts)

	      Minimum value: 0

	      Maximum value: 2,147,483,647

	      You can modify this attribute at run time.

	      Maximum number of vnodes (open files) on a system.

	      Default value: 1000 (for 24-MB systems); the number of vnodes that 5 percent of available memory can contain (for  32-MB	or  larger
	      systems)

	      Minimum value:  Specified by the nvnode attribute

	      Maximum value: The number of vnodes that 5 percent of physical memory can contain

	      Increasing  the value of the max_vnodes attribute allows more vnodes on a system, which may improve performance if your applications
	      or users create a large number of open files. Decreasing the value returns more memory to the system.

	      You can modify this attribute at run time. If you change the default value at boot time, the 5 percent maximum no longer applies.

	      Minimum number of free vnodes on the free list.  If the number  of  vnodes  on  the  free  list  is  less  than  the  value  of  the
	      min_free_vnodes attribute, vnodes are deallocated.

	      Default value: nvnode attribute (for 32-MB or larger systems); 150 (for 24-MB systems)

	      Minimum value: 0

	      Maximum value: 1,717,986,918

	      Increasing  the  value  causes  the  system to cache more free vnodes and may improve performance for vnode cache lookup operations.
	      However, a large value increases the demand for memory.

	      You can modify this attribute at run time.and

	      Size, in slots, of the hash chain table for the namei cache. By default, the value for name_cache_hash_size is automatically  scaled
	      according to the value of name_cache_size.

	      Default value: name_cache_size/8 or 8192 (whichever is smaller)

	      Minimum value: 0

	      Maximum value: name_cache_size/2

	      Large  hash  chain tables distribute the namei cache elements and may make chain lengths short, which can reduce linear searches and
	      improve lookup speeds.  In general, chains should contain only 2 or 3 elements.

	      Number of table elements in the hash chain table for the namei cache. The namei cache uses this hash chain table to  distribute  the
	      namei cache elements and minimize linear searches.

	      Default value: 2 * nvnode * 11/10 (for 32-MB or larger systems); 150 (for 24-MB systems)

	      Minimum value: 0

	      Maximum value: 2 * max_vnodes * 11/10

	      Increasing  the value of the name_cache_size attribute may improve lookup speeds, but it requires more memory.  Decreasing the value
	      can free memory.

	      To determine an appropriate value for the name_cache_hash_size attribute, divide the value of name_cache_size by 3  or  4  and  then
	      round down the result to a power of 2.  For example, if the value of name_cache_size is 1029, dividing 1029 by 4 produces a value of
	      257. Based on this calculation, you could specify 256 (2 to the power of 8) for the value of the name_cache_hash_size attribute.

	      Amount of time, in seconds, that a namei cache entry can remain in the cache before it is discarded.

	      Default value: 1200 (seconds) for 32-MB or larger systems; 30 (seconds) for 24-MB systems

	      Minimum value: 0

	      Maximum value: 2,147,483,647

	      A large namei-cache-valid-time attribute value will retain more vnodes references in the namei  cache and improve  the  namei  cache
	      lookup speed; however, it will require more memory resources.  A small value may cause premature deallocation of vnodes and decrease
	      the namei cache lookup speed.

	      Maximum number of record locks that may be held by a process. This limit prevents lock structures for any one process from consuming
	      too much kernel memory.

	      Default value: 10,000 (locks)

	      Minimum value: 1000

	      Maximum value: 100,000

	      You can modify this attribute at run time.

	      A  value	that enables (any positive value) or disables (0) the ability of users to create new executables on the system. This is an
	      enhanced security feature that is used, for example, on firewall systems. It does not affect performance. In a  TruCluster  environ-
	      ment,  this attribute must have the same setting on all cluster members. See the Security manual for more information about enhanced
	      security features.

	      Default value: 0 (disabled)

	      Obsolete in that it does not determine the maximum and the minimum number of vnodes on a system.	You should use the max_vnodes  and
	      min_free_vnodes attributes to adjust these mininum and maximum values.

	      Default value: nproc+(2*maxusers)+128

	      It  is  strongly recommended that you not change the default value of nvnode. The value of nvnode depends by default on the value of
	      maxusers, and this dependency should be left alone. Although the kernel uses the nvnode value to	calculate  the	default  value	of
	      other attributes, such as name_cache_size, you can change these attributes directly if there is a need to override their defaults.

	      A  value that enables (1) or disables (0) the ability of the telldir(3) and seekdir(3) routines to work on Network File System (NFS)
	      mounts from certain NFS vendors.	Enable this feature if your programs require this specific requirement. Once enabled, however, NFS
	      directory accesses might be less efficient.

	      Default value: 0 (disabled)

	      Size,  in  number of zone elements, of the pathname zone for pathname lookup buffers. Increasing the value of path_num_max increases
	      the number of elements in the zone that is allocated for pathnames.

	      Default value: 64 (zone elements)

	      Minimum value: 0

	      Maximum value: 2,147,483,647

	      Number of data bytes in each pipe data buffer.

	      Default value: 8192 (bytes)

	      Minimum value: 4096

	      Maximum value: 32,768

	      You can modify this attribute at run time.

	      Maximum number of bytes reserved for all pipes.

	      Default value: 134,217,728 (bytes)

	      Minimum value: 819,200

	      Maximum value: 1,717,986,918

	      You can modify this attribute at run time.

	      Maximum number of bytes buffered per pipe.

	      Default value: 262,144 (bytes)

	      Minimum value: 4096

	      Maximum value: 1,048,576

	      You can modify this attribute at run time.

	      A value that  determines	whether  the  revoke()	system	call  can  invalidate  file  descriptors  on  block  special  devices.	If
	      revoke_tty_only  is  set	to  1  (the  default), the revoke() argument must be a character (tty) device, and a block device argument
	      results in an [ENOTTY] error. If revoke_tty_only is set to 0, the revoke() argument can be either a character or a block device.

	      Default value: 1 (character devices only)

	      You can modify this attribute at run time; however, the default value is strongly recommended in a TruCluster environment.

	      Sets the amount of time, in seconds, that modified (dirty) pages can age before they must be written to disk.

	      Default value: 30 (seconds)

	      Minimum value: 0

	      Maximum value: 60

	      You can modify this attribute at run time.

	      Size (in number of hash-chain slots) of the special vnodes alias table for vnodes of special device files, such as character-I/O	or
	      block-I/O device files.

	      Default value: 64 (slots)

	      Minimum value: 0

	      Maximum value: 2,147,483,647

	      Increasing the size of the special vnodes alias table allows you to create more special device files.

	      A value that enables (1) or disables (0) strict POSIX conformance to clearing dirty file status for O_SYNC operations.

	      Default value: 0 (disabled)

	      The default provides better performance. Strict conformance to POSIX O_SYNC status flushing comes at a cost.

	      You can modify this attribute at run time.

	      Enables  (1) or disables (0) System V behavior when setting the group ID and file mode of created files and directories. By default,
	      the group ID of the file is set to the group ID of its parent directory. See open(2) for more information.

	      Default value: 0	(disabled)

	      Obsolete attribute.

	      Default value: 256

	      Amount of time, in seconds, that a vnode can remain on the free list before it is deallocated.

	      Default value: 120 (seconds) for 32-MB or larger systems; 2 (seconds) for 24-MB systems

	      Minimum value: 0

	      Maximum value: 2,147,483,647

	      You can increase the value of the vnode-age attribute to keep vnodes on the free list longer, which increases the  possibility  that
	      the vnode will be successfully looked  up.

	      You can modify this attribute at run time.

	      A value that enables (1) or disables (0) vnode deallocation.

	      Default value: 1 (enabled)

	      Enabling vnode deallocation decreases memory usage because it returns to the system the memory allocated to vnodes.

SEE ALSO

       Commands: dxkerneltuner(8), sysconfig(8), sysconfigdb(8)

       Others: sys_attrs(5)

       System Configuration and Tuning

																  sys_attrs_vfs(5)