Date: Thu, 24 May 2012 06:35:51 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Tim Kientzle <tim@kientzle.com> Cc: freebsd-hackers@freebsd.org, Matthias Apitz <guru@unixarea.de> Subject: Re: proper newfs options for SSD disk Message-ID: <alpine.BSF.2.00.1205240602540.53872@wonkity.com> In-Reply-To: <CF851064-F78F-44AF-B562-32012E4DC043@kientzle.com> References: <alpine.BSF.2.00.1205182209010.9350@wojtek.tensor.gdynia.pl> <4fb7dfd6.736a980a.186d.ffff902f@mx.google.com> <20120519180901.GA1264@tiny> <4fb7e819.6968700a.7a7f.ffff9153@mx.google.com> <20120522061734.GA1210@tiny> <alpine.BSF.2.00.1205220731070.51493@wonkity.com> <20120522134846.GA2274@tiny> <alpine.BSF.2.00.1205220837500.51493@wonkity.com> <CF851064-F78F-44AF-B562-32012E4DC043@kientzle.com>
next in thread | previous in thread | raw e-mail | index | archive | help
This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---902635197-107453168-1337862951=:53872 Content-Type: TEXT/PLAIN; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8BIT On Wed, 23 May 2012, Tim Kientzle wrote: > On May 22, 2012, at 7:40 AM, Warren Block wrote: > >> On Tue, 22 May 2012, Matthias Apitz wrote: >> >>> El día Tuesday, May 22, 2012 a las 07:42:18AM -0600, Warren Block escribió: >>> >>>> On Tue, 22 May 2012, Matthias Apitz wrote: >>>> >>>>> El día Sunday, May 20, 2012 a las 03:36:01AM +0900, rozhuk.im@gmail.com escribió: >>>>>> >>>>>> Do not use MBR (or manually do all to align). >>>>>> 63 - not 4k aligned. >>>>> >>>>> To create the above shown partition layout I have not used gpart(8); I >>>>> just said: >>>>> >>>>> # fdisk -I /dev/ada0 >>>>> # fdisk -B /dev/ada0 >>>>> >>>>> ... >>>>> What is wrong with this procedure? >>>> >>>> The filesystem partitions end up at locations that aren't even multiples >>>> of 4K. This can reduce performance. How much probably depends on the >>>> SSD. >>> >>> But this is then rather a bug in fdisk(8) and not a PEBKAC, or? :-) >> >> A bug in the design of MBR. Which probably can be forgiven, considering when it was created and the other problems with it. :) >> >> gpart's alignment option can be used with MBR slices and bsdlabel partitions. > > GPart's alignment option doesn't work for MBR slices. > It rounds to the requested alignment, and then rounds again > to the track size, which defaults to 63 sectors. There's an example in my proposed rewrite of the Handbook RAID1 section: http://www.wonkity.com/~wblock/mirror/book.html The slice starts at block 126, two blocks shy of 4K alignment. With the added two blocks for the bsdlabel, all of the FreeBSD partitions end up aligned at even 4K multiples. A filesystem in the raw slice would be misaligned. Presumably the answer is "well don't do that, then" (always use a bsdlabel with MBR), or some trick to skip a couple of blocks like gnop. If there are any mistakes in that example, please help me correct them to avert steps 4 and 5 of the traditional commit process (4: apologize, and 5: fix and recommit). > I'm not convinced this is a bug in the design of MBR. I don't > think anything in the MBR design requires that partitions > be track-aligned. I meant "bug" in the sense of a missing feature. MBR may not have a provision for fixed alignment, but to its credit, doesn't prevent it either. ---902635197-107453168-1337862951=:53872--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?alpine.BSF.2.00.1205240602540.53872>