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Date:      Wed, 27 Mar 2013 16:39:08 -0500
From:      Dan Nelson <dnelson@allantgroup.com>
To:        "Ronald F. Guilmette" <rfg@tristatelogic.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Copying memstick image to a USB (flash/thumb) drive
Message-ID:  <20130327213908.GA5447@dan.emsphone.com>
In-Reply-To: <6148.1364418621@server1.tristatelogic.com>
References:  <6148.1364418621@server1.tristatelogic.com>

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In the last episode (Mar 27), Ronald F. Guilmette said:
> I've never used any FreeBSD memstick image before, but now I have reason
> to do so.
> 
> I'm reading the instructions for creating a bootable memstick that are
> located on this page:
> 
>   http://www.freebsd.org/releases/9.1R/announce.html
> 
> which include the following example of how to perform the copy:
> 
>   # dd if=FreeBSD-9.1-RELEASE-amd64-memstick.img of=/dev/da0 bs=10240 conv=sync
> 
> Question:
> 
>    Why exactly is "conv=sync" is there?
>
> Question:
> 
>     Why exactly is the "bs=10240" is there?  Wouldn't the default of 512
>     do just as well?

It looks like someone just copied a dd commandline from somewhere else,
maybe something to do with tar files (since tar defaults to a 10k blocksize
when writing to tape).  conv=sync isn't needed since the source file is
already a multiple of the target device blocksize (512 bytes), and bs=64k
would be much faster when writing to cheap flash devices like USB sticks
since they don't have a write cache and individual writes are slowish.

-- 
	Dan Nelson
	dnelson@allantgroup.com



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