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presto(8)							    presto(8)



NAME

  presto - Controls and	monitors the Prestoserve file system accelerator

SYNOPSIS

  /usr/sbin/presto [options]

OPTIONS

  -d [filesystem ...]
      Disables Prestoserve and writes the Prestoserve cache data to the
      intended disks. If no file systems are specified,	all accelerated	file
      systems are disabled, and	the Prestoserve	state is set to	DOWN.

      The filesystem parameter can be used to disable specific file systems.
      You specify filesystem as	a directory mount point	(for example, /usr).
      If no file systems are specified,	all accelerated	file systems are dis-
      abled, and the Prestoserve state is set to DOWN.

      Do not specify a block device because some functional subsystems,	such
      as the Advanced File System (AdvFS), can map more	than one block device
      to a mount point.

      This option does not reset Prestoserve statistics.

      The -d option takes effect before	the -u or -R options.

  -D [filesystem ...]
      Similar to the -d	option,	but sets the Prestoserve state to DOWN only
      if the specified directory is the	root of	a mounted file system. Other-
      wise, the	following message is displayed:
	   presto: directory is	not a file system root

  -F  Flushes (writes) the Prestoserve cache data to the intended disks, but
      leaves the cache data intact.

      If the option is used and	the Prestoserve	state is UP, then the cache
      data is written to the intended disks, and the state remains UP. If the
      Prestoserve state	is DOWN, then there is no data to write	to the disks,
      and the state remains DOWN.  If the state	is ERROR, then as much of the
      cache data as possible is	written	to the intended	disks.

      Note that	unlike the -R option, the data in the Prestoserve cache
      remains after it is written to the intended disks.

  -l  Lists the	accelerated file systems and their mount points	in a format
      similar to the mount command.  This option can be	used with either NFS
      client or	server machines.

  -L  Lists all	mounted	file systems and their mount points that have been
      accelerated.  Any	unusual	Prestoserve state for a	file system is
      displayed	after the mount	point. The unusual states include:

      bounceio
	  Instead of directly accessing	the nonvolatile	memory,	the file
	  system's device receives the Prestoserve data	only after the data
	  is first copied to main memory.

      disabled
	  Prestoserve acceleration is not enabled on the file system.

      error
	  An error occurred using the file system, and the Prestoserve cache
	  data has still not been written successfully to the intended disks.

  -p  Displays Prestoserve information.	 The information includes the current
      Prestoserve state; the statistics	for write, read, and total opera-
      tions; and battery status.  For example:
	   # /usr/sbin/presto -p
	   dirty = 52, clean = 7, inval	= 903, active =	2
		  count	hit rate clean hits dirty hits allocations passes
	   write:  1516	     65%	  0	   989	       511     15
	    read:     8	      0%	  0	     0		 0	8
	   total:  1524	     65%	  0	   989	       511     23
	   state = UP, size = 0x7e000 bytes
	   statistics interval:	00:00:13  (13 seconds)
	   write cache efficiency: 66%
	   All batteries are ok

      The current Prestoserve statistics account for all Prestoserve buffers.
      A	dirty buffer contains a	disk block image that has not been written to
      disk.  A clean buffer contains a valid disk block	image that has been
      written to disk.	An inval buffer	does not presently contain a disk
      block image.  An active buffer is	currently in transition	to disk,
      meaning that a write operation has started but has not completed on
      that buffer.

      For each Prestoserve cache read or write operation, Prestoserve incre-
      ments a counter, as follows:

	+  The clean hits counter shows	the number of hits (block matches) on
	   the clean buffers.

	+  The dirty hits counter shows	the number of hits on the dirty
	   buffers. Each dirty hit on a	write represents a physical disk
	   write that was avoided entirely, while a hit	on a read represents
	   a physical disk read	that was avoided.

	+  The allocations counter shows the number of new buffers that	had
	   to be allocated for disk block images.

	+  The passes counter shows the	number of I/O operations that Pres-
	   toserve passed directly to the real device driver.

      In addition, for each Prestoserve	cache read or write operation, the
      presto -p	command	displays the count, which is the sum of	the four
      counters explained previously; the hit rate percentage, which is the
      ratio of clean hits and dirty hits to the	total count and	which indi-
      cates the	effectiveness of the Prestoserve cache;	and the	write cache
      efficiency percentage, which is computed from the	ratio of write dirty
      hits to the number of writes copied into the Prestoserve cache.

      The presto -p command also displays information about the	Prestoserve
      battery state.  The command displays the battery state as	ok, low, or
      disabled.

      Some processors support chargeable batteries and use self	tests to
      determine	if a battery needs charging. If	you use	the presto -p command
      on a machine that	supports chargeable batteries, the battery state can
      also be in self test or is charging. Note	that if	you use	the dxpresto
      command, batteries that are being	self-tested or charged will be
      displayed	as disabled.

  -R  Writes as	much of	the Prestoserve	cache data as possible to disk,
      discards the data	it could not write, purges all the Prestoserve
      buffers, and sets	the Prestoserve	state to DOWN.

      Unlike the -d option, the	-R option discards the Prestoserve cache data
      that could not be	written	to disk	and resets the statistics informa-
      tion. The	option is useful when Prestoserve cache	data is	not needed or
      if you cannot get	Prestoserve out	of the ERROR state.


				      Caution

	 Take care when	using the -R option, because it	destroys Prestoserve
	 cache data.

      The -R option takes effect before	the -u option.

  -s size
      Sets the size of the Prestoserve cache to	size bytes.  The size can be
      specified	using the decimal or hexadecimal conventions.  For example,
      both 262144 and 0x40000 represent	256 Kbytes.

      If the -s	option is used and the current Prestoserve state is UP,	the
      state is set to DOWN, the	Prestoserve cache is resized, and the state
      is set to	UP.

      You may want to use the -s option	to determine how Prestoserve performs
      with a reduced amount of nonvolatile memory.  Note that the size of the
      Prestoserve cache	cannot be larger than the default maximum size or
      smaller than the default minimum size.  If you specify a size that is
      larger than the default maximum size, the	default	maximum	size is	used.
      If you specify a size that is smaller than the default minimum size,
      the default minimum size is used.

  -u [filesystem ...]
      Sets Prestoserve state to	UP, and	enables	acceleration.

      If no file systems are specified,	all local writable file	systems	that
      are mounted will have Prestoserve	enabled.  File systems that are
      presently	accelerated will remain	accelerated.

      The filesystem parameter can be used to enable specific file systems.
      You specify filesystem as	a directory mount point	(for example, /usr).

      Do not specify a block device because some functional subsystems,	such
      as the Advanced File System (AdvFS), can map more	than one block device
      to a mount point.

      If Prestoserve state was ERROR, Prestoserve attempts to write any
      blocks that are in the cache to disk to ensure that the previous error
      condition	has been corrected.

  -U [filesystem ...]
      Similar to the -u	option,	but sets the Prestoserve state to UP only if
      the specified directory is the root of a mounted file system. Other-
      wise, the	following message is displayed:
	   presto: directory is	not a file system root

  -v  Specifies	verbose	mode.  This option prints extra	information to stan-
      dard output.  The	information can	be used	for debugging purposes.


DESCRIPTION

  The presto command allows you	to accelerate file systems, obtain Pres-
  toserve status, and administer Prestoserve.

  If invoked with no options, presto displays the Prestoserve state (either
  UP, DOWN, or ERROR), the number of bytes of nonvolatile memory the Pres-
  toserve cache	is using, how long the cache has been enabled, the write
  cache	efficiency, and	the state of the backup	battery	or batteries.

  When the Prestoserve state is	UP, Prestoserve	improves I/O performance to
  accelerated file systems by caching synchronous disk write operations	to
  nonvolatile memory.

  When the Prestoserve state is	DOWN, all I/O requests are passed to the
  appropriate disks.

  If it	detects	a disk error during a write back, Prestoserve enters the
  ERROR	state and disables itself.  However, Prestoserve continues to main-
  tain the integrity of	cached data.  Some possible disk error conditions
  are:	the disk drive is write	protected or off line, a cable problem
  exists, or a bad disk	block exists.

  Also,	if there is insufficient backup	battery	power, Prestoserve will	enter
  the ERROR state.

FILES

  /dev/pr0
      Generic Prestoserve control device.

SEE ALSO

  Commands: prestoctl_svc(8), prestosetup(8), dxpresto(8X)

  Files: prestotab(4)

  Networking: presto(7)

  Guide	to Prestoserve