Subject: Re: Another changer, another changer problem
To: NetBSD-current Discussion List <firstname.lastname@example.org>
From: Curt Sampson <email@example.com>
Date: 10/02/1998 20:27:21
On Fri, 2 Oct 1998, Greg A. Woods wrote:
> if someone gives me a printout of /etc/fstab and two powered down
> machines and tells me to move the spindles associated with one specific
> database from one machine to another (assuming a one-2-one mapping of
> the databse filesystems and spindles), I should be able to do that
> without first powering up the machine.
Well, it's not likely you're going to. Given an Adaptec and a
Buslogic controller, each on the PCI bus can you tell me which one
will be attached first? Will the order of the attaching change if
you reverse the slots? If the two controllers are the same, can
you tell from the motherboard which slot is the lowest numbered?
If your controllers are on different buses, it gets even worse
because you have to know the bus attach order, which may vary
depending on machine architecture and BIOS/Boot PROM. And Lord help
you if you're on a bus such as P&P ISA, where the probe order is
indeterminate; each card in that case has its own driver-dependent
order to attach in.
This is why we have single-user mode; your best bet is to boot the
machine up with all the disks attached, and rewrite your fstab or
build a new kernel that has the proper attachments hardwired.
> I should also be able to edit
> the /etc/fstab from single user mode on both machines and get it right
> without having to copy down the probe messages since I should be able to
> know with 100% certainty what /dev nodes correspond to the removed/added
Well, you Just Can't; see above.
> LUNs are simply logical volumes -- equivalent to partitions but managed
> by the external device, not the device driver in the kernel.
Well, if you're going to take the view that the two disks, one to
a LUN, on the Emulex controller in my Sun shoebox are `logical
volumes,' why not say that both disks on the SCSI controller in my
PC are `logical volumes'?
Curt Sampson <firstname.lastname@example.org> 604-257-9400 De gustibus, aut bene aut nihil.
Any opinions expressed are mine and mine alone.
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