dumping a raid member with 'dd' for insurance...

[Chuck Swiger]

Hi--

On May 11, 2010, at 3:35 PM, George Sanders wrote:
> [ ... ]
> I am planning on attaching each individual member of the raid5 array to a test FreeBSD system, and run:
> 
> dd if=/dev/ad1 of=/data/disk/image.file
> 
> Two questions:
> 
> - is that a complete 'dd' command, or do I need to specify "bs=xxx" and "count=xxx"  ?

What you've suggested should work as-is.  Adding the count option isn't useful, but specifying a bs of 64k or larger will considerably speed up the process of copying the data.  Since you're dealing with a failed array and it's possible some of the disks might have errors when read, using conv=noerror might also be a good idea.

> - is there any chance that simply booting with this drive attached to the system, and running a 'dd' like this, will somehow alter the contents or "touch" the array member in any way ?  What I have described above appears to be a completely read-only process, but I'd like to make sure there aren't ANY bits that FreeBSD will write to this disk ...

Many disks have a write-protect jumper which you can use to make sure no changes get written.

Regards,
-- 
-Chuck