defragment man page on DigitalUNIX

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defragment(8)							 defragment(8)

       defragment - Makes the files in a file domain more contiguous

       /usr/sbin/defragment  [-e]  [-n]	 [-N threads] [-t time] [-T time] [-v]
       [-V] domain

       Ignores errors and continues, if possible. Errors that are ignored  are
       usually related to a specific file.  Specifies the number of threads to
       run on the utility.  The default number of threads that will be run  is
       the  number of volumes in the domain.  The maximum number you can spec‐
       ify for the number of threads is	 20.   Prevents	 defragmentation  from
       actually taking place. Use in conjunction with the -v option to display
       statistics on the number of extents in the file	domain.	  Specifies  a
       flexible	 time interval (in minutes) for the defragment utility to run.
       If the utility is performing an operation when the specified  time  has
       elapsed,	 the  procedure	 continues  until  the	operation is complete.
       Specifies an exact time interval (in minutes) for the defragment	 util‐
       ity  to	run.  When the specified time has elapsed, the defragmentation
       procedure stops, even if it is performing an operation.	Displays  sta‐
       tistics	on the amount of fragmentation in the file domain and informa‐
       tion on the progress of the defragment procedure.   Displays  the  same
       information provided by the -v option along with information about each
       operation the defragment utility performs on each  file.	  This	option
       slows the defragment procedure.

       Specifies the name of the file domain.

       When  a	file  consists of many discontiguous file extents, the file is
       fragmented on the disk. File fragmentation reduces the read/write  per‐
       formance	 because  more	I/O  operations are required to access a frag‐
       mented file.

       The defragment utility attempts to reduce the number of file extents in
       a  file	domain	by  making files more contiguous. Defragmenting a file
       domain often makes the free space on a disk more contiguous,  resulting
       in less fragmented file allocations in the future.

       Before  you  can	 defragment  a	file  domain, all filesets in the file
       domain must be mounted. If you try to defragment an active file	domain
       that  includes unmounted filesets, the system displays an error message
       indicating that a fileset is unmounted.

       To determine the amount of file fragmentation in a file domain, run the
       defragment  command with the -v and -n options. This provides the frag‐
       mentation information without starting the defragmentation process. Run
       defragment with the -v and -n options again to see the improvement.

       Before  running	the defragment utility, delete any files in the domain
       that you do not need. This gives the defragment utility more free space
       to  use, which produces better results.	Deleting files afterwards cre‐
       ates only more free-space fragments. It is also a good idea to run  the
       balance	utility on the domain before you run the defragment utility in
       order to balance domain free  space  before  defragmenting  the	domain

       To  monitor  the	 improvement made to the file domain by the defragment
       utility, use the verbose mode option, -v, which displays the  following
       information: Extents

	      The  number  of  extents	in  the	 specified domain. (Contiguous
	      extents in sparse files are counted as one extent after  defrag‐
	      mentation,  when	in  fact  there	 are  several  contiguous file
	      extents.)	 Files w/ extents

	      The number of files that have extents. (Note that files  do  not
	      have  extents if the files are less than 7 Kilobytes.)  Avg exts
	      per file w/ exts

	      The average number of extents for each file that has one or more
	      extents.	Aggregate I/O perf

	      The  efficiency  of the entire file domain. An increase in value
	      indicates improvement.  Free space fragments

	      The number of free-space fragments in the domain.

       The defragment utility requires a minimum of 1  percent	of  the	 total
       space, or 5 megabytes per volume (whichever is less) to defragment that

       You must be the root user to use this utility.

       You cannot run  the  defragment	utility	 while	the  addvol,  balance,
       defragment,  rmfset,  or	 rmvol	utility	 is  running  on the same file

       If the vfast utility is activated and defragment, balance, or topIObal‐
       ance  are  enabled  on that domain, then the standard AdvFS balance and
       defragment utilities are not available.

       Running the defragment -nv command on a domain with a large  amount  of
       metadata	 can  cause it to fail. To prevent this from happening, double
       the size of per_proc_data_size with the sysconfig command  or   specify
       the doubled value in the /etc/sysconfigtab file.

       The  following example defragments the file domain called accounts_dmn.
       A flexible time limit of 15 minutes is  imposed	and  verbose  mode  is
       requested  to  display  the  fragmentation  data: # defragment -v -t 15

       defragment: defragmenting domain 'accounts_dmn'

       Pass 1; Clearing

	 Volume 1: area at block    11680 (  103072 blocks): 81% full
	 Domain data as of the start of this pass:
	   Extents:		     10432
	   Files w/extents:	      4305
	   Avg exts per file w/exts:  2.42
	   Aggregate I/O perf:	       52%
	   Free space fragments:      2743
			    <100K    <1M    <10M    >10M
	     Free space:     38%      0%      0%     62%
	     Fragments:	    2742       0       0       1

       Filling .  .  .	Pass 13; Clearing
	 Volume 1: area at block   559744 (   62736 blocks):  0% full
	 Volume 2: area at block    76640 (   24624 blocks): 18% full
	 Domain data as of the start of this pass:
	   Extents:		      4306
	   Files w/extents:	      4305
	   Avg exts per file w/exts:  1.00
	   Aggregate I/O perf:	      100%
	   Free space fragments:	23
			    <100K    <1M    <10M    >10M
	     Free space:      0%      9%     27%     64%
	     Fragments:	       6      10       5       2


	 Current domain data:
	   Extents:		      4305
	   Files w/extents:	      4305
	   Avg exts per file w/exts:  1.00
	   Aggregate I/O perf:	      100%
	   Free space fragments:	17
			    <100K    <1M    <10M    >10M
	     Free space:      0%      6%     29%     65%
	     Fragments:	       3       8       4       2

       defragment: defragmented domain 'accounts_dmn'

       The information displayed before each pass and at the conclusion of the
       defragmentation	process	 shows the improvement made to the file domain
       by the defragment utility.

       Commands: addvol(8), balance(8), rmvol(8), vfast(8)


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