I'm going to post this to the whole list, because it is so dramatic. The
only question that matters here is, "Is it an email inbox? yes or no."
If the answer is Yes, the daily change rate approaches 100%.

Roger Deschner      University of Illinois at Chicago     rogerd AT uic DOT edu


On Fri, 4 Jun 2004, Steve Harris wrote:

>Hi All,
>
>I'm trying to size TSM servers for some small remote sites that we have.  In 
>the past, with more primitive products, one of the issues has been getting 
>staff in these locations - generally nurses - to physically change tapes.  For 
>that reason, and to avoid the cost of a library, I'm looking at a disk primary 
>pool and tape copypool, with db back ups up the wire to a "mother" site.
>
>I've written a program that models the TSM backup and expiry process. Some 
>assumptions are a  small daily update rate, but a file changed yesterday is 
>50% likely to be changed today and 25%  if it was changed in the last week.  I 
>realize in the real world that there are weekly and monthly cycles too, but 
>I've left them out for the model for simplicity.
>
>With a 1% daily change rate, 35 day retention and no compression, I'll need 
>5.7 times the original data space (thats steady state average +3 standard 
>deviations), but the number is quite sensitive to the daily rate of change
>
>1%      5.7
>1.25%   6.5
>1.5%    7.1
>1.75%   7.9
>2%      8.6
>2.5%    9.8
>3%      10.7
>5%      13.2
>10%     16.9
>
>At the moment, I don't back up any File servers, so I have no idea what a 
>usual rate of change might be.
>
>First, can anyone comment on my assumptions.
>
>Second, can anyone share change rates for file servers with a normal load of 
>office workers creating word processing docs, spreadsheets, etc.  I understand 
>that Netware changes attributes in situations where Windows does not, so if 
>you could say which type of OS you are using that would be handy too.
>
>Rather than flood the list, email direct to me at steve_harris AT 
>health.qld.gov DOT au and I'll summarize.
>
>
>Thanks
>
>Steve Harris
>AIX and TSM Admin
>Queensland Health,
>Brisbane Australia
>
>
>
>
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