Re: Linux vs. NetBSD disk enumeration

[Jeff Rizzo <riz%tastylime.net@localhost>]

On 2/9/12 10:45 AM, Manuel Bouyer wrote:
> Yes, it's because drives are numbered in the order they're found.
> We have the same issue with e.g. hot-swap bays; if you insert a new drive
> in the middle of a bay the drives can be renumbered on next boot.

Yes, I'm aware of that.

> /dev/sda1 will be translater to the linux's block device number. This 
> is what xen uses as 'id'. In my config files I don't use linux's 
> devices names but 0x0, 0x1, 0x2, .... Up to now I've never seen a 
> NetBSD kernel probe xbd is random order: the xen tools create the 
> entries in the xenstore in the domains's config file order, and the 
> domU kernel reads the xenstore sequentially. 

Does this block device number remain consistent every time?  Is there 
any way we can use it in the kernel as a locator for xbd*?

OK, I'm not 100% sure what's going on, but I'm sure it's because Amazon 
have their own method of putting the devices in xenstore.

Here's the dmesg from an instance I just tried;  two of the xbd devices 
are ones I normally use (and which reliably and consistently show up as 
xbd0/xbd1 when I only use them), and two are ones I added for this 
test.  Unfortunately, it doesn't print any information about them but 
their xenbus id, so I'm not even certain which one gets mapped where.

NetBSD 5.1.2 (XEN3PAE_DOMU) #0: Thu Feb  2 17:18:36 UTC 2012
        
builds%b6.netbsd.org@localhost:/home/builds/ab/netbsd-5-1-2-RELEASE/i386/201202021012Z-obj/home/builds/ab/netbsd-5-1-2-RELEASE/src/sys/arch/i386/compile/XEN3PAE_DOMU
total memory = 1700 MB
avail memory = 1662 MB
mainbus0 (root)
hypervisor0 at mainbus0: Xen version 3.4
vcpu0 at hypervisor0: Intel 686-class, 2266MHz, id 0x106a5
xenbus0 at hypervisor0: Xen Virtual Bus Interface
xencons0 at hypervisor0: Xen Virtual Console Driver
xencons0: using event channel 2
npx0 at hypervisor0: using exception 16
xbd0 at xenbus0 id 2049: Xen Virtual Block Device Interface
xbd1 at xenbus0 id 2080: Xen Virtual Block Device Interface
xbd2 at xenbus0 id 2050: Xen Virtual Block Device Interface
xbd3 at xenbus0 id 2051: Xen Virtual Block Device Interface
xennet0 at xenbus0 id 0: Xen Virtual Network Interface
xennet0: MAC address 12:31:38:1b:a9:b6
raidattach: Asked for 8 units
Kernelized RAIDframe activated
Searching for RAID components...
boot device: xbd1
root on xbd1a dumps on xbd1b
mountroot: trying lfs...
mountroot: trying ffs...
mountroot: trying ext2fs...
Ext2 fs: unsupported inode size
mountroot: trying nfs...
mountroot: trying smbfs...
mountroot: trying ntfs...
mountroot: trying msdos...
mountroot: trying cd9660...
mountroot: trying coda...
no file system for xbd1 (dev 0x8e08)
cannot mount root, error = 79
root device (default xbd1a):