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Re: DD not working--SUCCESS!



imalone:
>> How would you go about estimating a decent blocksize (other than by
>> testing)?  My first instinct would be to go for some percentage of
>> the drive's cache.

Jacques B:
> Available RAM.  Use as big a block size as can possibly be read into
> RAM (once you start caching to a drive you just as well be writing to
> the destination drive otherwise you slow it down even more).  We
> played around with this a while back and it certainly makes a
> difference (stands to reason as was already explained).
> 
> The one caveat would be if there are errors on the drive.  If that is
> the case, a full block is dropped (so if your block size is 4096
> bytes, then 4K gets dropped instead of 512 bytes - now imagine
> dropping a 256 meg block of data...).  ddrescue will use two block
> sizes - a larger one and a smaller one.  If it hits an error it drops
> back to the smaller one until it gets pass the error and then ramps
> back up to the larger block size.

I had a little play around with blocksizes for dd a while ago, while
zeroing a drive (I was zeroing out a bad drive to see it it'd goad the
drive into automatically sorting out the bad blocks, by itself - it
did).  The first attempt just started out using the default, and that
took ages.  After a bit of fiddling, I settled for using about a meg.

Of course my situation was a bit different, but it's to show that you'd
tweak the option to suit your circumstances.

-- 
[tim bigblack ~]$ uname -ipr
2.6.22.4-65.fc7 i686 i386

Using FC 4, 5, 6 & 7, plus CentOS 5.  Today, it's FC7.

Don't send private replies to my address, the mailbox is ignored.
I read messages from the public lists.




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