Re: UUID vs /dev
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Bob McGowan wrote:
> Michael Pobega wrote:
[snip]
>>
>> I think UUID is used because it is better to use UUID to recognize the
>> drives than /dev. For example, if you're trying to have your USB drive
>> automount to /mnt/usb, you'd use something like "/dev/sdb1" in fstab,
>> correct? What if you plug in an external drive? That will be picked up
>> at /dev/sdb, and following that the USB thumbdrive will be picked up as
>> /dev/sdc. The reason for UUIDs is to make it so that the computer can
>> recognize the drives by their device ID rather than the order they were
>> plugged in.
>>
>> I may be wrong though. This is what I've been told.
>>
>
> This is correct, but is a 'high overview' level description. A few more
> details, maybe, will help understanding what's going on (and the only
> downside I know for it).
>
> First, the UUID and LABEL methods work in basically the same way, but
> the UUID is generally considered better, particularly for drives that
> migrate between systems (such as USB or Firewire). There is less of an
> issue with colliding values between multiple systems using the UUID.
>
> On booting, the system scans devices and determines the UUID (or LABEL),
> and creates symlinks from the UUID/LABEL directories (/dev/disk/by-uuid
> or /dev/disk/by-label) pointing to the actual device node associated
> with the UUID/LABEL.
>
> So the system can find a device node, using the LABEL or UUID. Once
> found, the system uses the device node. It's this that leads to the
> single 'downside' that I've seen, of using UUID/LABEL:
>
> Once mounted, the system 'forgets' the UUID/LABEL, so output of the
> 'mount' command lists device nodes. Same for 'df'.
>
> And, KwikDisk (KDE applet) will show two items for a particular mount
> point, the content from fstab (LABEL/UUID) and the device node actually
> mounted and used to access the device. It's pretty quickly obvious (for
> the moderately experienced user) which element to use to umount the
> device, but the multiple entries can become confusing if you have
> several disks or partitions set up this way.
Thanks Bob, for the clear explanation.
Now I understand why in Windows when one wants to "safely remove" a
device it shows a list of things that make it very hard to figure out
what to click on. That of course has little bearing on my now since I
dumped my MS baggage.
I can understand the usage of UUID on removable drives, but it seems the
new way of dealing with *all* disks is UUID. Why this needs to be so
for normal hard drives remains a mystery to me.
Joe
- --
Registerd Linux user #443289 at http://counter.li.org/
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