Index for Section 8

Alphabetical listing for C

chvol(8)
NAME
  chvol - changes the attributes of a volume

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

OPTIONS
  -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 768 blocks.
      For optimal performance, specify blocks in multiples of wblks (as
      specified by the -w option).

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

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

  -A  Activates a volume after an incomplete rmvol operation.

OPERANDS
  special
      Specifies the block special device name, such as /dev/rz2c.

  domain
      Specifies the name of the file domain.

DESCRIPTION
  The chvol command enables you to change the attributes of a volume in an
  active domain.  For example, the file system can consolidate a number of
  I/O transfers into a single, large I/O transfer.  The larger the I/O
  transfer, the better the file-system performance. If you attempt to change
  the attributes of a volume in a domain that is not active, an error
  messages is produced.


  The initial I/O transfer parameter for both reads and writes is 128 blocks.
  Once you change the I/O transfer parameters with the -r option or the -w
  option, the parameters remain fixed until you change them. 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.

  For file system workloads that are heavily biased toward random writes, use
  the -t option to increase the file system's dirty threshold. This may
  improve file write performance.

  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
       parameters of the /dev/rz1c volume in the domain1 file domain:
	    # chvol /dev/rz1c domain1
	    rblks = 128	 wblks = 128  cmode = on

   2.  The example also toggles the cmode:
	    # chvol -c off /dev/rz1c domain1
	    # chvol /dev/rz1c domain1
	    rblks = 128	 wblks = 128  cmode = off

   3.  The example continues by changing the I/O transfer parameters of reads
       (rblks) and writes (wblks) from 128 blocks to 256 blocks.  Note that
       the cmode is off and must be on before the parameters take effect:
	    # chvol -r 256 -w 256 -c on /dev/rz1c domain1
	    # chvol /dev/rz1c domain1
	    rblks = 256	 wblks = 256  cmode = on



SEE ALSO
  advfs(4), showfdmn(8)