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Re: USB3 3TB HDD boot

From: Lennart Sorensen
Subject: Re: USB3 3TB HDD boot
Date: Fri, 15 Mar 2013 13:53:43 -0400
User-agent: Mutt/1.5.20 (2009-06-14)

On Fri, Mar 15, 2013 at 09:59:22AM -0600, Chris Murphy wrote:
> How would it?
> These structures are still predicated on a 512 byte block. The MBR is always 
> 512 bytes, but on a 4096/4096 4Kn drive, LBA 0 is 4096 bytes. So if I don't 
> want to see 3584 bytes of useless garbage, I can't set the dd block size to 
> 4096, or I get extra information.

Well if you want to get LBA 1 on a 4096 byte sector device, using dd
bs=4096 skip=1 count=1 would get that sector and make it more obvious
which sector you are getting (to me at least).

So yeah you get extra stuff that way, but it is what is really there
after all.  If you only wanted 92 bytes you could have used a bs=128 as
well and gotten even less junk.

> If I want to see just the GPT header, which while only ~92 bytes, by spec it 
> gets its own sector, there's far less superfluous information using a bs of 
> 512 bytes than 4096 bytes.

True, although the drive has to read 4096 bytes no matter how much you
ask for.

Len Sorensen

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