Date: Mon, 27 Aug 2012 20:51:52 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Kevin Oberman <kob6558@gmail.com> Cc: Erich Dollansky <erichfreebsdlist@ovitrap.com>, freebsd-stable@freebsd.org, Stefan Bethke <stb@lassitu.de>, Matt Smith <matt@xtaz.co.uk> Subject: Re: 9.1 RELENG_9 Unable to cleanly dismount root partition on shutdown Message-ID: <alpine.BSF.2.00.1208272031570.73072@wonkity.com> In-Reply-To: <CAN6yY1vLm7Cbri-1JoJs2dd9=jgYQRp0WPFB3c-wDyHv6vY95Q@mail.gmail.com> References: <2d4dfcb2637f4d0e9671899538b603d9@xtaz.co.uk> <67DFAA78-A9A2-49F9-9C29-CA5653ECE3C0@lassitu.de> <b98001dbe576eafcf4f4500e975680ec@xtaz.co.uk> <20120827172650.7e6a7685@AMD620.ovitrap.com> <c5c51c674a29c136f0d10a3fe936a6a0@xtaz.co.uk> <alpine.BSF.2.00.1208270750130.46223@wonkity.com> <78f8335e54e04f158609f0382afb8d4d@xtaz.co.uk> <alpine.BSF.2.00.1208271230360.48366@wonkity.com> <CAN6yY1u1bJm_dBNKx4_rZkhgpevX6ovm1cyPeu5%2B929HSZWvZQ@mail.gmail.com> <alpine.BSF.2.00.1208271356560.49435@wonkity.com> <CAN6yY1vLm7Cbri-1JoJs2dd9=jgYQRp0WPFB3c-wDyHv6vY95Q@mail.gmail.com>
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On Mon, 27 Aug 2012, Kevin Oberman wrote: > On Mon, Aug 27, 2012 at 1:16 PM, Warren Block <wblock@wonkity.com> wrote: >> On Mon, 27 Aug 2012, Kevin Oberman wrote: >> >>>> No obvious problems jumped out at me. Here are my notes: >>>> http://www.wonkity.com/~wblock/docs/html/disksetup.html >>>> >>>> The gpart version is halfway down. I really need to switch that around. >>> >>> >>> Pretty good page, but I would really suggest that you also do either >>> 4k or 1M alignment on your partitions. If you don't and use a disk >>> with 4K blocks (internally), you will have terrible performance. >> >> >> You mean add the -a parameter for gpart? All that -a does is round >> partition starting blocks and sizes to even values. If the numbers given >> are already even multiples, it does nothing. > > You can force alignment by use of -b. I just managed to miss that you > were doing that. '-a' simply does the alignment and I have no reason > to forces the location of any partition as all are multiples of 1M and > 4K. Use of -a and -b on the same command seems rather useless, Might make more sense if -a is seen as a safety check. And yes, -b is an exception, done in this case to get the first partition at a specific spot. > but it seems that ignoring -b is still a bug. Works for me in 9-stable. Here's the change in -head: http://svnweb.freebsd.org/base/head/sbin/geom/class/part/geom_part.c?r1=229916&r2=235033 It was MFCed to 8-stable and 9-stable on 2012-05-11. > I'm not sure I get your statement that "All that -a does is round > partition starting blocks and sizes to even values. " -a aligns the > start of every partition to the stated size (as your example showed). Sorry, I should have been more precise with the wording. By "even" I meant even multiple of the given block value. >> The reason -a4k is not shown there is because until a few months ago, -a >> overrode -b. So >> >> # gpart add -t freebsd-ufs -l gprootfs -a4k -b 1M -s 2G da0 >> >> did not start that partition at 1M, but instead at the next even 4K block >> after the first 512K partition; block 1064 instead of block 2048, AFAIR. >> The fix to gpart (thanks to ae@) is in 9-stable and 9.1, but not earlier >> releases. >> >> Mentioned a little farther down in the article is that keeping additional >> partitions to even multiples of 1M or 1G size will keep them in alignment. >> >>> 1M is recommended by Microsoft and used by Windows, but seems a bit >>> excessive to me. >> >> >> Also by some Sun RAID controllers and other systems. 1M is a nice even >> multiple of a lot of common block sizes. > > True, but so is 4K (8-512 byte blocks). Obviously 1M is also a > multiple of all powers of 2 below it as is 4K. Even in this age of > cheap disks, 1G alignment seems a bit extreme, but in most cases, it Er, 1M. It leaves a little less than 512K of unused space. Starting at 1G would be a more difficult decision for me, though you're right that it's a trivial amount of space on a lot of computers. > really is insignificant for general purpose systems. It is an argument > for single partitions, but I always worry that something screwy will > blow up /var with log messages and I would not want this to fill all > disk space, so I like to keep that, as well as a read-only root. Just > old-fashioned, I guess. Understood. Usually separate filesystems for me, although I recently took to using tmpfs for /tmp.
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