From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Landman Subject: Re: The chunk size paradox Date: Thu, 02 Jan 2014 22:14:41 -0500 Message-ID: <52C62B21.2090609@gmail.com> References: <52C1C01A.7010407@ubuntu.com> <52C57C7B.80400@shiftmail.org> <52C588A7.6010207@hardwarefreak.com> <52C59468.6080200@ubuntu.com> <52C5A9AA.9090300@hardwarefreak.com> <52C5BC28.2020003@gmail.com> <52C5EB62.1090807@hardwarefreak.com> <52C5EE8F.3090204@aei.mpg.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <52C5EE8F.3090204@aei.mpg.de> Sender: linux-raid-owner@vger.kernel.org To: Carsten Aulbert , stan@hardwarefreak.com Cc: Phillip Susi , joystick , linux-raid List-Id: linux-raid.ids On 01/02/2014 05:56 PM, Carsten Aulbert wrote: > Hi > > sorry late in joining the thread Hey Carsten, good to see you here! > > On 01/02/2014 11:42 PM, Stan Hoeppner wrote: >> >> Damn, you had me salivating Joe. These are both AF 512e drives, not >> native 4K. >> >>> and many others. >> >> I've not yet seen an announcement from anyone. I'm not all seeing, but >> I'd think such an announcement would cross my RADAR. >> > > Just look around: > > > http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771475.pdf > > and then the FAQ about "Advanced Format": > > https://wdc.custhelp.com/app/answers/detail/a_id/5655 > > Why would one need to align to 4k if the on disk layout would be 512bytes? > > Or did I miss something? If you align to a 1k size (2x 512 byte emulated sectors), then you will be offset from the start of the real 4k sector. As you can see from the WD document, advanced format drives are 4k with a 512byte translation layer. They are there specifically to provide backwards compatibility for old OSes. For best performance, they recommend using the units in their native 4k format. But they are 4k native and you can use them that way. The 512 byte layer is emulated.