Date: Sat, 15 Feb 2014 08:54:44 +0100 From: Ulf Lilleengen <lulf@freebsd.org> To: freebsd-geom@freebsd.org Cc: Warren Block <wblock@wonkity.com>, ae@freebsd.org, marcel@freebsd.org, freebsd-geom@freebsd.org Subject: Re: Allowing arbitrary MBR slice alignment Message-ID: <7737397.rILaIf05sy@nobby> In-Reply-To: <alpine.BSF.2.00.1402140918560.88288@wonkity.com> References: <alpine.BSF.2.00.1402140918560.88288@wonkity.com>
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On Friday 14. February 2014 09.24.34 Warren Block wrote: > The Problem > > More and more disk devices have native 4K blocks. The ability to align > MBR slices to arbitrary values is consequently becoming more important. > Misaligned filesystems might read or write at less than half the speed > of aligned filesystems on the same disk. > > Microsoft recognized this problem, and at least since the release of > Vista in 2007, MBR-formatted disks created by Microsoft operating > systems have started the first or main filesystem slice at block 2048 > (1M). Despite the official standard for MBR alignment to CHS values, > this second non-CHS but 4K-aligned de facto standard has become > extremely common. *snip* > Suggested Solution > > gpart(8) should be allowed to override the CHS rounding with -a and -b > values when creating MBR slices. If CHS rounding occurs when the > options are not given, gpart(8) should give a warning that default > values were used to avoid surprising the user. > > The warning is really secondary. Primarily and pragmatically, gpart(8) > needs the ability to create MBR slices with arbitrary alignment so > FreeBSD can deal gracefully with modern storage hardware. > IMHO, 4k alignment should be default in freebsd as well, unless there are some actual disadvantages for the users. I think the majority of users would like good performance. But allowing to override it is a good start :) Ulf
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