On Tue, 2007-10-23 at 18:31 -0600, Karl Larsen wrote: > 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! > > > 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? Ah! I'd expect that. The kernel will generally say that the drive that contains / (the root) will be the first drive (/dev/sda). Where the other drives end up depends on how fast the drives spin up and go ready, the order the buses are scanned, etc. and as I said, that can vary from kernel to kernel. When you boot the second drive, it becomes /dev/sda (since / is on THAT drive), hd1 is seen before other drives go ready/are scanned, etc. and becomes /dev/sdb. Yes, it's confusing. ---------------------------------------------------------------------- - Rick Stevens, Principal Engineer rstevens@xxxxxxxxxxxx - - CDN Systems, Internap, Inc. http://www.internap.com - - - - Do not taunt the sysadmins, for they are subtle and quick to anger - ----------------------------------------------------------------------
