Date: Wed, 19 Nov 2014 15:32:11 +0100 From: Mark Martinec <Mark.Martinec+freebsd@ijs.si> To: freebsd-stable@freebsd.org Subject: Re: 10.1 fresh install and 4k alignment Message-ID: <ead753e90b2b74b169af2fb04c525c9e@mailbox.ijs.si> In-Reply-To: <A2328132-EC43-4E27-8D01-A4D774634598@punkt.de> References: <A2328132-EC43-4E27-8D01-A4D774634598@punkt.de>
next in thread | previous in thread | raw e-mail | index | archive | help
Patrick M. Hausen wrote: > Hi, all, > > I just installed a new machine with 10.1-RELEASE using the memstick > installer > and chosing ZFS mirror root as the disk layout. > > I did check the "4k" option, watched the installer do the necessary > gnop dance > and the pool seems to be OK: > > root@seleniumhub:~ # zdb | grep ashift > ashift: 12 > > But this puzzles me a bit: > > root@seleniumhub:~ # gpart list ada0 > Mediasize: 524288 (512K) > Sectorsize: 512 > ... > Providers: > 1. Name: ada0p1 > Mediasize: 524288 (512K) > Sectorsize: 512 > ... > end: 1057 > start: 34 > ... > 3. Name: ada0p3 > Mediasize: 465747565056 (434G) > Sectorsize: 512 > ... > type: freebsd-zfs > ... > end: 976773134 > start: 67109922 > > None of the start sector numbers is a multiple of 8, neither are the > end sectors > a multiple of 8 minus 1. > > So the pool uses a 4k block size but it starts on an odd multiple of > 2k on the platter > - do I see this correctly? > > Isn't it absolutely necessary that the simulated 4k blocks are laid > out so that the first > is made from 512 byte sectors 0-7, the second from 8-15 and so on? > > Then why does the installer start the first partition at 512 byte > sector 34? While I'm at > it, this magic number is everywhere in the older documentation, e.g. > for manually > installing FreeBSD 8 with gptzfsboot - where does that 34 come from? > It's not > a power of 2 nor is it one of the historical CHS magic numbers that > would mean > a cylinder boundary or similar. Size of the GPT partition table itself? > > Is this a bug in the installer? Will I still have to layout the disks > manually if I want 4k > alignment? What's a good offset for the first partition in this case? > Anything bigger > than 34 that's a multiple of 8 - 40 or 64? > > Thanks in advance > Patrick Reported on 2014-10-10, but was apparently forgotten/ignored: "GPT partitions not 4k aligned by 10.1-RC1 installer" https://lists.freebsd.org/pipermail/freebsd-stable/2014-October/080509.html Mark
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?ead753e90b2b74b169af2fb04c525c9e>