/dev/sda and /dev/hda

[Karl Larsen]

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 at 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.