Thanks to everyone who replied to this. Most helpful indeed.
Farren :) Please respond to "ADSM: Dist Stor Manager" <[EMAIL PROTECTED]> Sent by: � � � �"ADSM: Dist Stor Manager" <[EMAIL PROTECTED]> To: � � � �[EMAIL PROTECTED] cc: Subject: � � � �Re: Question about database fragmentation If your system is at all large, fragmentation is just a way of life. After a while, it will not get any worse. Except when you do a lot of filespace deletions at once, as Paul Seay said, or if expiration breaks for a while and is then repaired, it will get out of kilter, but that is a self-healing problem. It will work itself back towards its normal steady-state fragmentaion, eventually. (Disclaimer!) I _THINK_ it will. You can't fix it without more downtime than you can afford, and it's not easy to measure, either. SOMEBODY PLEASE TELL ME IF I'M COMPLETELY WRONG, but my observation is that there are two kinds of fragmentation in the TSM database. 1) The B-tree gets unbalanced and fragmented 2) The pages that contain active parts of the structure become fragmented across too many blocks. BOTH kinds of fragmentation are harmfull in that they increase seek distances to get to the data, and increase the number of disk seeks to get a group of data items which are logically together. I do not know how to measure the first kind of fragmentation, except for the painful and lengthly UNLOAD/RELOAD process and then see how much it shrinks. This will take "until the cows come home" or whatever expression you use for "much too long". However, the second kind of fragmentation is more easily measured. Do Q DBVOL F=D and add up the "Allocated space" for all of them. Divide that into the total Avalable Space, and you'll get a percentage. The difference between that percentage and the Percent Utilization shown by Q DB is how badly disk pages are fragmented across disk blocks. The SECOND kind of fragmentation, BUT NOT THE FIRST, can be cured by DELETE DBVOL. This is still a time-consuming process, but at least it can be done with TSM up and available to clients, albeit running slow. What I have described, about two different kinds of fragmentation, is from observations on my own system, not from any information from anybody else. If this is wrong, somebody please tell me a different way to interpret what I am observing. But, to summarize, it is probably not worth worrying too much about Database fragmentation, because there is not much you can afford to do about it, and it really is not hurting performance all that much, compared to some of the glaring configuration mistakes you can make. Roger Deschner � � �University of Illinois at Chicago � � [EMAIL PROTECTED] ==== "Research is what I'm doing when I don't know what I'm doing." ==== ========================= -- Wernher von Braun ========================= On Wed, 2 Oct 2002, Seay, Paul wrote: >The only way to reorganize the database is an UNLOADDB, LOADFORMAT, LOADDB. >Nothing else accomplishes this. �If your database has had lots of filespace >deletions the tree can get severly unbalanced and negatively affect >performance. > >Paul D. Seay, Jr. >Technical Specialist >Naptheon Inc. >757-688-8180 > > >-----Original Message----- >From: Farren Minns [mailto:[EMAIL PROTECTED]] >Sent: Wednesday, October 02, 2002 9:47 AM >To: [EMAIL PROTECTED] >Subject: Question about database fragmentation > > >Hi All > >I wonder who can help me with this. Does the database become very fragmented >over time? If so, is there any way of telling how much? Also, is the only >fix for this to do a dump and reload of the database? > >If the answer to the final question is yes, how easy are dump/reloads? > >We recently upgraded from TSM 3.7.3.8 to 4.2.2.12 and had to run an auditdb >first (which completed without any problems). > >Many thanks in advance > >All the best > >Farren Minns - TSM and Solaris System Admin - John Wiley and Sons Ltd > >Our Chichester based offices have amalgamated and relocated to a new address > >John Wiley & Sons Ltd >The Atrium >Southern Gate >Chichester >West Sussex >PO19 8SQ > >Main phone and fax numbers remain the same: >Phone +44 (0)1243 779777 >Fax � +44 (0)1243 775878 >Direct dial numbers are unchanged > >Address, phone and fax nos. for all other Wiley UK locations are unchanged > **************************************************************************** >** > Our Chichester based offices have amalgamated and relocated to a new address John Wiley & Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ Main phone and fax numbers remain the same: Phone +44 (0)1243 779777 Fax +44 (0)1243 775878 Direct dial numbers are unchanged Address, phone and fax nos. for all other Wiley UK locations are unchanged ******************************************************************************
