dd flag - choosing appropriate block size

William Muriithi william.muriithi-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org
Sun Sep 7 14:21:28 UTC 2008


Morning there,

I have googled for the logic one use to pick the appropriate block
size for dd and I have to say I am still a little lost. Yes, I have
used dd a couple of time before but I always copy it from somewhere on
the net and then change if and of. That mean, I may have been messing
up with block size and slowed down the transfer.

Now what encouraged me to read more on it is the realization a wrong
block size can even be more harmful. See the quote below.

 "Note:
Care has to be taken when specifying the block size bs as exact
multiple of the physical size of the device because improper block
size will result in data inconsistency, or overlap."

http://64.233.169.104/search?q=cache:88BW3Dok8NUJ:publib.boulder.ibm.com/infocenter/systems/topic/com.ibm.aix.cmds/doc/aixcmds2/dd.htm+dd+bs%3D*&hl=en&ct=clnk&cd=12&gl=ca

Problem now is, you may not always know the physical block size of the
device and when you have that information, arriving at the best
multiple is not well explained.  Would it be better to not specify the
bs when one is not sure?


Regards,

William
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