Re: 2.7 block ramblings (was Re: DMA for ide-scsi?)

[Jeff Garzik <jgarzik@pobox.com>]

Andries Brouwer wrote:
> Such things are infinitely difficult.
> Moreover, great care is needed - one has to define precisely what it
> is this GUID is supposed to be an ID of.

Absolutely agreed.


> (Is it the ZIP drive? Or is it the ZIP disk?
> The 2.4 USB code is broken because it remembers a GUID and thinks that
> identical GUID implies identical disk.)
> 
> I have a handful of CF/SM cardreaders.
> Some of them have no form of ID. Others have an ID.
> 
> Then one can insert a CF or SM card into the reader.
> Some of these cards have an ID. Some have not.
> 
> On the card one usually finds a FAT filesystem.
> There may be a label. Or there may not be.
> 
> This describes a 3-level situation.
> I have also 4-level situations, where the reader is filled with
> one of four auxiliary adapters (each with an own ID) and the
> adapter then get a CF/SM/SD/... card.

Using an adapter's ID would be a mistake.  You want to use the media's 
unique ID, assuming it has one.


> So, yes, we love IDs. And we can always provide them ourselves
> as label or UUID or so in the filesystem.

Not all filesystems have them :)

Further, some sites may prefer block-level GUIDs to fs-level ones. 
Sites using raw partitions instead of filesystems, for one.

We must leave this up to the sysadmin -- within the bounds of technology 
of course.  The sysadmin is out of luck if they purchase a media that 
does not support some sort of labelling or UUID.


> But finding an unformatted unlabeled disk is difficult.

You sound like you're agreeing with me ;-)

	Jeff