At date and time Thu, 19 Jun 2014 21:51:12 -0400, Greg Troxel wrote: > > Gerard Lally <lists+netbsd.us...@netmail.ie> writes: > > > 1) Is it safe to use GPT on NetBSD? The warnings on the gpt man page > > leave me less than 100% confident. > > On NetBSD 6, I would say yes. Even on 5, I think so. I am not really > clear on booting from GPT, but for other than the boot/root fs it should > be fine. I have multiple systems with gpt disks and no issues. > > > 2) As I understand it the NetBSD FFS filesystem is capable of growing > > to 8 zettabytes, but MBR partitioning combined with traditional > > disklabels meant we were restricted to 2 (or 4) TB partitions in > > practice. Am I right in saying that GPT and wedges remove this > > restriction, and we can now create partitions and filesystems greater > > than 4TB? > > I think disklabels are limited to 2TB; I'm not sure if it's the whole > disk or per partition. (Maybe that's 4TB.) That is correct - GPT does > not have a 2TB limit.
That's great. It will be a while before I get >2TB disks for my data but I'm glad the restrictions won't be there when I do. > > 3) Using "NAME=dk0" in /etc/fstab didn't work for me; I had to specify > > /dev/dk0, /dev/dk1, etc. > > > > This is not a big deal but it leaves me wondering how NAME=xxx in fstab > > is supposed to work. Does it work with GPT labels instead? > > My impression is that NAME matched the gpt label, so you could mount a > disk with label foo on /volumes/foo repeatedly. > > > 4) To get the sector offsets and sizes right I first created a > > traditional MBR + disklabel setup, sizing partitions in MB and taking > > note of the sector offsets and sector sizes this produced. I started at > > 2048. After destroying the MBR + disklabel setup I then used this > > information to create GPT partitions. I assume this is a safe way to do > > it? I am not really familiar with partition alignment, and even less so > > since the new disks came out. > > In the modern world, disks don't really have consistent geometries. So > the big alignment issue is to make sure that you line up on physical > blocks, which are often 4K (on disks 2T and greater, or maybe 1T or > greater). And, there is some threat of larger physical sizes later. > > So, two recommendations are: > > start the first partition at some multiple of 64 (because it's a > multiple of any sane near-term size). > > start the first partition at 1 MB (2048 * 512 sectors), which is an > even rounder number, and is still a negligible space waste. (This > really surprised me when I did the math; I remember using 2.5 MB > disks.) > > Whatever you do - don't start things at sector 34, which is the start of > available space. Here's "gpt show" from a 1T disk I have in use. Note > that I didn't worry about the exact size being round. > > start size index contents > 0 1 PMBR > 1 1 Pri GPT header > 2 32 Pri GPT table > 34 30 > 64 1953525071 1 GPT part - NetBSD FFSv1/FFSv2 > 1953525135 32 Sec GPT table > 1953525167 1 Sec GPT header > > > So I really don't see why you are making disklabels and then > transferring numbers. Just make all the start and size values a > multiple of 2048 sectors, for some size that's round in binary, or close > to what you want. Or live on the edge at 64 like I did (I'm kidding; I > don't think there's anything wrong with 64). Well I did it that way because I hadn't really looked into sizing partitions by sector before, but when you mentioned it I went off and learned how to do it, using basic maths. Very straightforward actually. Thanks! > If you find the man pages saying things that are wrong, feel free to > send a patch fixing it. Yes I would like to start contributing back to NetBSD, but it will be mostly documentation (English and Philosophy were my subjects). -- Gerard Lally