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chvol(8)							     chvol(8)



NAME

  chvol	- Changes the attributes of a volume

SYNOPSIS

  /sbin/chvol [-l] [-r blocks] [-w blocks] [-t blocks] [-c on |	off] [-A]
  special domain

OPTIONS

  -A  Activates	a volume after an incomplete addvol or rmvol operation.

  -c on	| off
      Turns I/O	consolidation mode on or off.

  -l  Displays the range of I/O	transfer sizes,	in 512-byte blocks, as calcu-
      lated by the kernel, based on the	disk's geometry:

      rblks displays the minimum, the maximum, and the preferred transfer
      size for reads.

      wblks displays the minimum, the maximum, and the preferred transfer
      size for writes.

  -r blocks
      Specifies	the maximum number of 512-byte blocks that the file system
      reads from the disk at one time.

  -t blocks
      Specifies	the maximum number of dirty, 512-byte blocks that the file
      system will cache	in-memory (per volume in a domain).  Dirty means that
      the data has been	written	by the application but the file	system has
      cached it	in memory so it	has not	yet been written to disk.

      The number of blocks must	be in multiples	of 16. The valid range is 0-
      32768. The default (when a volume	is added to a domain) is 16,384
      blocks. For optimal performance, specify blocks in multiples of wblks
      (as specified by the -w option) and multiples of rblks (as specified by
      the -r option).

  -w blocks
      Specifies	the maximum number of 512-byte blocks that the file system
      writes to	the disk at one	time.

OPERANDS

  special
      Specifies	the block special device name, such as /dev/disk/dsk2c.	This
      command supports shorthand device	names for block	special	devices. For
      example, if you enter dsk2g, it will be translated to /dev/disk/dsk2g.

  domain
      Specifies	the name of the	domain.






DESCRIPTION

  The chvol command can	be run at anytime to change the	attributes of a
  volume in an active domain; the system does not have to be quiescent.	If
  you attempt to change	the attributes of a volume in a	domain that is not
  active, an error message is produced.

  The initial I/O transfer parameter for both reads and	writes is typically
  128 or 256 blocks, depending on the disk driver's preferred I/O transfer
  rate.	 Once you change the I/O transfer parameters with the -r option	or
  the -w option, the parameters	remain fixed until you change them again. The
  values for the I/O transfer parameters are limited by	the device driver.
  Every	device has a minimum and maximum value for the size of the reads and
  writes it can	handle.	If you set a value that	is outside of the range	that
  the device driver allows, the	device automatically resets the	value to the
  largest or smallest it can handle.

  By default, the I/O consolidation mode (cmode) is on.	 The cmode must	be on
  for the I/O transfer parameters to take effect. You can use the -c option
  to turn the cmode off, which sets the	I/O transfer parameter to one page.

  Interrupting an rmvol	operation can leave the	volume in an inaccessible
  state. If a volume does not allow new	allocations after an rmvol operation,
  use the chvol	command	with the -A option to reactivate the volume.

  Using	the chvol command without any options displays the current cmode and
  the I/O transfer parameters.

RESTRICTIONS

  The values for the wblks and rblks attributes	are limited by the device
  driver.

  You must be the root user to use this	command.

EXAMPLES

   1.  The following example displays the cmode	and the	I/O transfer parame-
       ters of the /dev/disk/dsk1c volume in the domain1 domain:
	    # chvol /dev/disk/dsk1c domain1
	    rblks = 128	 wblks = 128  cmode = on thresh	= 16,384

   2.  The following example additionally toggles the cmode:
	    # chvol -c off /dev/disk/dsk1c domain1
	    # chvol /dev/disk/dsk1c domain1
	    rblks = 128	 wblks = 128  cmode = off thresh = 16,384

   3.  The following example continues by changing the I/O transfer parame-
       ters of reads (rblks) and writes	(wblks)	from 128 blocks	to 256
       blocks.	Note that the cmode is off and must be on before the parame-
       ters take effect:
	    # chvol -r 256 -w 256 -c on	/dev/disk/dsk1c	domain1
	    chvol /dev/disk/dsk1c domain1
	    rblks = 256	 wblks = 256  cmode = on thresh	= 16,384

   4.  The following example shows the I/O transfer range on domain1:
	    # chvol -l /dev/disk/dsk0a domain1
	    chvol /dev/disk/dsk0a domain1
	    rblks: min = 16  max = 32768  pref = 256
	    wblks: min = 16  max = 32768  pref = 256






SEE ALSO

  Command: showfdmn(8)

  Files: advfs(4)