On Saturday 15 November 2008, lee <[EMAIL PROTECTED]> wrote about 'Re: udev causing data loss?': >On Sat, Nov 15, 2008 at 10:42:52AM -0700, ghe wrote: >> At the time of my misadventure, I was still expecting sda to be the >> lowest ID on the lowest SCSI bus -- there were no SATAs at the time, >> not around here anyway. > >That is what I would expect. Are you saying that there is no way to >tell which disk is which one from the device names?
Depends. Stuff in /dev/disk/by-uuid has never lead me astray.
However /dev/sd* nodes are named in the order the device is detected by
the kernel. It's not like that label is written to the disk.
I believe that disks on a single SCSI bus are always detected in order by
increasing SCSI id. However, /dev/sd* also includes USB and SATA devices,
probably some others, too. Devices are now probed asynchronously ("in
parallel"; which makes the kernel boot faster), so the USB disk that you
left in the system might be assigned a name before your SCSI bus. Any of
your two SCSI buses and one SATA bus could be assigned name(s) first and
this could vary from boot to boot.
>If that is true, how does the user, how does the system know which
>disk is which one?
Well, the system assigns those names as it detects devices. It gets some
input from the user via their udev configuration.
>As user, I can eventually tell with fdisk -l and
>looking at the info --- *if* the disks are all different. But how does
>the system figure out if the device refered to in /etc/fstab is
>actually the device that should be refered to?
The system has no notion of "should be". The system uses the device name
you list in /etc/fstab. It's the administrator's responsibility to make
sure that's what should be referred to.
Personally, I like using UUID= syntax to refer to my devices
(/dev/disk/by-uuid doesn't list logical volumes), but it does make the
lines in /etc/fstab a bit long. The LABEL= syntax is also a good one.
>It seems I need to read up on this. Is there a good document that
>explains it?
You can start with man udev, then a quick google for "linux udev how-to",
but I don't really know a definitive document.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
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