Making a bootable backup (hard)disk... how?

Warren Block wblock at
Mon Jun 11 00:36:33 UTC 2012

On Sun, 10 Jun 2012, Robert Huff wrote:

> Ronald F. Guilmette writes:
>>  Warren?  Just a couple more quick questions.  You recommend:
>> >>   dump -C16 -b64 -0uanL -h0 -f - /usr | (cd /mnt && restore -ruf -)
>>  I'm real curious about you suggestions for the -C and -b values.
>>  I have what amounts to a personal workstation.  Yea, OK, it is running
>>  mail, web, and FTP servers also, but fundementailly, it is not that busy
>>  most of the time.  And it's got 4GB of main installed.  On average, I
>>  suspect that I ain't even using half of that.
>>  Given all that, why shouldn't I specify (e.g.): -C512 -b1024  ?
>>  Wouldn't that all make the dump go faster?
> 	There are many possible obstacles to faster dump speed;
> enumerating them is left as an exercise for the reader.
> 	As it happens, I have a set-up very similar to what you
> describe ... except with 8g of memory.  A few years ago I did some
> testing with various cache sizes (as part of diagnosing other
> problems) and ended up with C=32.
> 	(I should probably run the tests again, given some hardware
> changes since.)
> 	That machine's level 0 runs tonight; I will try to remember to
> (retain and) post the results.

-C16 is a little small because it's hard to tell how much memory someone 
running the example will have.  I usually use -C32 on machines with 
plenty of memory.  Remember that dump forks multiple times, so it's not 
32M, but N*32M.

-b64 is the largest safe buffer size to use.  People have experienced 
problems with larger amounts.

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