Date: Fri, 4 Jan 2013 14:30:44 -0700 (MST) From: Warren Block <wblock@wonkity.com> To: Christian Weisgerber <naddy@mips.inka.de> Cc: freebsd-questions@freebsd.org Subject: Re: bsdinstall misaligns partitions Message-ID: <alpine.BSF.2.00.1301041423210.7774@wonkity.com> In-Reply-To: <kc72kq$158v$1@lorvorc.mips.inka.de> References: <kc72kq$158v$1@lorvorc.mips.inka.de>
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On Fri, 4 Jan 2013, Christian Weisgerber wrote: > Shouldn't bsdinstall attempt to align partitions on 4k boundaries > both for the benefit of 4k drives and flash storage? I think the latest version does. > I just installed 9.1R i386 for fun and practice, in fact I installed > it several times, and I played around with the partitioning options. > > * The modern GPT scheme reserves 34 sectors at the start of the disk. > Your newly created partitions will start at offset 34 and will > therefor be misaligned. I ended up configuring a 63 kB freebsd-boot > partition, which ensures that the following partitions are aligned. > > * The old MBR scheme is even worse. The FreeBSD slice will start > at sector 63, guaranteeing that any partitions contained within > will be misaligned. There is no way to fix this, unless you > shell out and run fdisk manually. Even worse news: you can't fix it manually. Both fdisk and gpart are slaves to the kernel code that deals with MBR layouts, and will align to the old CHS values. I have not found a way to use FreeBSD to create an MBR slice that starts at 1M, block 2048. The CHS alignment always forces it to block 2079, a multiple of 63. However, gpart's -a alignment flag will offset BSD partitions within the slice so they are aligned. > * Funnily enough, the ancient BSD "dangerously dedicated" scheme > is the only one that out of the box does not misalign partitions. The filesystems don't begin at the start of the slice anyway. There is a bsdlabel there. > I'm presumably not the first one to notice this issue, and yes, I'm > mostly just venting. A way to override the CHS alignment would be welcome.
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