Subject: Re: Large disks and NetBSD 4.0?
To: Ronald Roskens <>
From: Jukka Marin <>
List: netbsd-users
Date: 10/27/2007 09:46:44
On Fri, Oct 26, 2007 at 06:04:45PM -0500, Ronald Roskens wrote:
> On Fri, 2007-10-26 at 14:14 +0300, Jukka Marin wrote:
> > I will try setting up a new server with a 3 TB (or so) RAID disk to be used
> > for XEN virtual machines.  What is the best way of partitioning the disk -
> > is it possible to disklabel disks this big in the normal way or should I be
> > using wedges or something?  Do wedges work with XEN?
> While I'm still new to setting up Xen under netbsd, here's some things
> I've learned:
> 1- NetBSD as a domU sees the disk you give it as a "real" disk.
> While you might assign the domU /dev/raid0e, and further bsdlabel that
> partition inside the domU, accessing a particular filesystem under dom0
> isnt easy.

Well, at this moment I'm mostly worried about FFS and multiple terabyte
disks - does FFS support them and is it reliable?  I have a 3ware RAID
controller and six 1 TB disks, so NetBSD will probably see a single 5 TB
disk (if I decide to configure a 6-disk RAID5 system).  Will this work?

I think I'll have to get one more disk and first install NetBSD on that
disk and then play with the 5 TB disk for a while.

> Makes it hard if you dont have networking setup between the domU's to
> transfer files around, or just want to mount up a domU's filesystems.

I think I can live with that, if NetBSD just supports the 5 TB disk.

> 2- The standard XEN3_DOM{0,U} kernels do not include the options for
> DKWEDGE_* and drvctl.

grep didn't find "wedge" in any kernel config file.

> wedges seem to be pretty cutting edge, and theres not a lot of
> documentation written about them. In particular, the ptype argument for
> dkctl addwedge isnt well defined. The types arent the same as their
> disklabel versions. (ie: ffs = 4.2BSD, lfs = 4.4LFS)

Yep, I noticed that there is no howto - I find any other documentation
but two or three man pages.  I have no idea if the system can boot from
a large disk with wedges on it (is the boot program able to find a kernel

> You need to use gpt to create a GPT on the disk, but raidframe devices
> do not seem to be supported. If your not using raidframe, then GPT would
> seem to give you the flexibility in terms of the number of partitions it
> would support as wedges.

GPT?  Never heard :)

> The combination of the 2 above have made me decide to do everything
> using vnd files.

I may try that, too, but I wonder how big the loss in performance is
when compared to raw partitions?  (Well, my current server is a 700
MHz raid frame system, so the new one will probably be faster even
with vnd files..)

> 3- For grub, if your root device isnt automatically detected in the dom0
> (say root is on wd2a rather than wd0a), you need to specify rootdev=X
> rather than root=X.


So, can anyone tell whether FFS works ok on a 5 TB disk or if I should
use some other method (and if so, what)?