Re: question about fstab in squeeze and uuid
On 20100313_144620, Stephen Powell wrote:
> On Sat, 13 Mar 2010 00:26:58 -0500 (EST), Paul E Condon wrote:
> >
> > A bit worrisome to me. UUID must be persistent during normal life of a
> > device, so it can be used as an identifier.
>
> It is important to distinguish between a device and a partition.
> /dev/hda is a device. /dev/hda1 is a partition. Partitions
> can be created, deleted, moved, resized, reformatted, etc. many
> times during the life of its containing device. The UUID of a
> partition is assigned when the partition is formatted, either with
> mkfs or mkswap. It retains this value until it is formatted again,
> at which time a new UUID is calculated. I don't know what the
> algorithm is for computing a UUID for a hard disk partition.
> Of course, reformatting a partition destroys all data on it; so in
> that sense it starts a new life with a new identity.
>
I'm learning. One thing I discovered today is that in extN, a disk
label (i.e. what you see when you type ls /dev/disk/by-label ) can
have multiple values on a single disk. This label is stored in the
partition table data of the several partitions. I haven't yet
discovered what is done with the excess volume labels, or what, if
any, confusion results from having multiple values. So ... its not
quite true that there is a device and a partition. I know its a
'distinction without a difference', this sort of thing is confusing
when one is trying to figure stuff out from incomplete information.
Also, both mke2fs and tune2fs are capable of setting the UUID of a
partition, either to a software computed value or a user supplied
value. And dumpe2fs -h or tune2fs -l will display the UUID setting
along with other partition parameters.
Some things that I firmly believed a few hours ago, I now know are
absolutely not true. What I will firmly believe a few hours from now
remains to be seen.
Thanks.
--
Paul E Condon
pecondon@mesanetworks.net
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