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Conference star::wizards

Title:	"ASK THE WIZARDS"

Moderator:	QUARK::LIONEL

Created:	Mon Oct 30 1995
Last Modified:	Mon May 12 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	1857
Total number of notes:	3728

1828.0. "Open: defragger?" by STAR::JKEENAN () Wed Apr 30 1997 15:23

Date: Wed, 30 Apr 1997 13:05:25 -0400
Message-Id: <[email protected]>
From: "VMS001::WWW"@vms001.das-x.dec.com (30-Apr-1997 1305)
To: [email protected], [email protected], [email protected]
Subject: Ask the Wizard: '[email protected]'

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Name: Flo Berry - Bromenn Healthcare
Email Address: [email protected]
CPU Architecture: Alpha
Version: V 6.2
Questions:

I understand that  DEC may have a defragger that runs in 
background mode(??).  Since we are a 24/365 operation it's
hard to take users off the system for great lengths of time
and certainly be interested in this type of defragger.  We
have files that are constantly being changed that causes
95% fragmentation monthly.  In the past, system maintenance
was done monthly to backup and restore the drive of choice
to keep from degrading response time....hence -- the need
for a defragger to run in background mode -- perhaps in the
early AM hours when the load is lighter.  Any suggestions?
or -- any other products that work with the ALPHA 4100?
Appreciate the help.

T.R	Title	User	Personal Name	Date	Lines
1828.1		MOVIES::WIDDOWSON	Rod OpenVMS Engineering. Project Rock	`Thu May 01 1997 06:08`	9
	Digital sell a product call(ed?) POLYCENTER DFO which allows you to defragment filesystems as an online operation. This has a limitation that open files cannot be defragmented. Some third parties have products which they claim can defragment open files and which they claim are safe. Digital only supports defragmentors which use the MOVEFILE primitive which cannot defragment open files. Usually fragmentation can be reduced (but not fully controlled) by careful application design.
1828.2	_Guide to OpenVMS File Applications_	XDELTA::HOFFMAN	Steve, OpenVMS Engineering	`Thu May 01 1997 14:33`	31
	Some level of fragmentation is entirely normal and expected. As mentioned, I would evaluate why the files are being fragmented, and what can be done -- via SET FILE/EXTEND, via SET RMS, via code changes, via changes in file structures used, or via various other means -- to reduce the file fragmentation on these files where it actually matters. I would also evaluate which specific files tend to be most quickly fragmented. Log files, for instance, can generally tolerate higher fragmentation levels, as logs are seldom accessed, and are seldom accessed in performance-critical situations. Indexed files can fragment on a disk as the files are extended, and can also "fragment" within the file structure within the file itself as records are deleted. Scratch files, and files that grow in small increments over long intervals, could be placed on seperate disk spindles, to reduce inter-application fragmentation, and to ease cleanup. Files that change less often -- such as the OpenVMS operating system files -- can also be placed on a seperate disk spindle. Defragmentation tools such as DFO can assist with reducing file-level fragmentation, but cannot assist with tasks such as cleaning up the deleted records in the internal structure of an indexed file. For an introduction to some of these concepts, see the _Guide to OpenVMS File Applications_ manual.