using dd to copy my freebsd partion to another drive

Chuck Swiger cswiger at
Sun May 25 09:43:21 PDT 2003

D Velez wrote:
[ ...]
> but all have different block sizes and I am confuse. I see some as
> bs=512 bs=1024 bs=8192, etc....
> Is there a way to calculate the block size of the
> two hard drives myself or is there a standard
> block size to use for any hard drive, cdrom and floppy.

Many devices actually have physical 512-byte sectors (not CD's and DVD's 
though), so 512 is the closest thing to a "standard" block size.  People 
commonly use larger block sizes because multi-sector reads go faster in 
most circumstances.  Try comparing bs=512 and bs=5120 and see for yourself.

Also, note that dd is best used when the source and destination are 
identical: if your other drive is a different size, you might find using 
dump and restore to be a better bet.


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