dump level 9

[Jerry McAllister]

> 
> Jerry McAllister wrote:
> 
> >But, I wonder why you chose level 9 for your change dumps.   It sort 
> >of defeats the system.   It would be more normal to use level 1.    
> >I know that [some much] earlier versions of BSD dump only took levels 
> >up to 5, but I presume that since they include up to 9 in the documentation
> >it should work.
> >  
> >
> If you only use one level other than 0, then it makes no difference what 
> that level is: 1, 9, 5 anything but 0.  A level N dumps everything since 
> the last dump < N, which in this case is always the last level 0.

Of course, but then you limit yourself from moving to a level 2 or
higher to accomodate an especially large change dump the day before.


> Using "modified tower of hanoi" (so the man page says :-)) can decrease 
> the amount of data per dump at the cost of having to do more dumps: e.g. 
> I do 0: 1 3 2 1 3 2 ... 0 ...  But if I have to restore everything and 
> the last dump was a 2, I have to restore the 0 1 and 2.  Similarly if it 
> crashed after 3, I would do 0 1 3.  That cuts down the amount of data 
> dumped, but is slightly more complex than just having to restore the 0 
> and last 9 (in the OPs case).  I could use 1 7 9, or 4 6 8 instead of 1 
> 2 3 and the data dumped would be the same in each case.

The simplest, if you do a weekly full dump and daily change dumps
is 0, 1, 2, 3, 4, 5, 6
but of course, that mean doing the most restores, though possibly
smaller ones, of all the schemes.   It doesn't work, of course, if
you only do a monthly full dump and daily change dumps.

> I was pretty sure that BSD 4.2 had 9 incremental dump levels, but that 
> was long, long ago in a universe of 1600bi tapes far, far away :-)

I don't know just when it was, but back then I was working on
vendor's proprietary flavors of BSD, so it could have been their
particular flavor, although I am pretty sure they just took utilities
like dump and simply recompiled and used them as is.

////jerry

> 
> --Alex
> 
>