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Re: /dev/sda and /dev/hda



Rick Stevens wrote:
On Tue, 2007-10-23 at 17:50 -0600, Karl Larsen wrote:
Rick Stevens wrote:
On Tue, 2007-10-23 at 17:13 -0600, Karl Larsen wrote:
As I have been working with 2 hard drives I have discovered for certain that both hard drives change to /dev/sda when a partition on them is booted. It happens that one is found at /dev/sdf and the other is found at /dev/sdb. This leads to confusion and in my case I am not sure what to think.

Is this changing the disk drives a feature or is it a bug? If not a feature I will write a bug soon.

    I understand the /dev/hda stays the first hard drive.
Well, sorta.  Depends on the kernel you're booting.  On earlier kernels
(pre-F7), IDE drives remained /dev/hdX.  Under F7 and later kernels,
ALL block storage is treated as SCSI (/dev/sdX) regardless of how it's
physically connected.  There's no differentiation at that level (there
is in sysfs, but let's not go there right now).

If you have other devices that were treated as SCSI before (USB, SATA,
whatever), your IDE stuff now gets added to the mix and the names can
change.  You also have to remember that grub uses a TOTALLY DIFFERENT
drive naming convention than a Linux kernel does.

Also note that in the Linux kernels, /dev/sdX refers to the ENTIRE
drive--not a partition on the drive.  /dev/sda is the first SCSI
disk (the ENTIRE disk), /dev/sda2 is the second partition on the first
SCSI disk.
I'm sorry but you are avoiding the question. I say /dev/sdf changes to /dev/sda when booted. Is this a feature or a Bug?

I didn't mean to.  How did you determine it was /dev/sdf first if the
system hadn't booted?  I think I'm missing something here.

Note also that different kernels may scan the buses in different orders
which may move things on you.  The same kernel on different hardware can
do different things as well.  For example, on Dell 1850s with NICs in
the PCI slots, the PCI slot NICs get eth0 and eth1, the mobo NICs get
eth2 and eth3.  On 2850s, the mobo NICs get eth0 and eth1 and the PCI
NICs get eth2 and eth3.

Ah, consistency!

----------------------------------------------------------------------
- Rick Stevens, Principal Engineer             rstevens internap com -
- CDN Systems, Internap, Inc.                http://www.internap.com -
-                                                                    -
-      On a scale of 1 to 10 I'd say...  oh, somewhere in there.     -
----------------------------------------------------------------------

OK again. If I run fdisk from hd 1 which is booted I find hd 2 is at /dev/sdf and hd 1 is at /dev/sda. If I boot from hd2 I find it is at /dev/sda now and hd1 has changed to /dev/sdb.

    Is this a feature or a Bug?


--

	Karl F. Larsen, AKA K5DI
	Linux User
	#450462   http://counter.li.org.


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