[Stgt-devel] Store persistent media data in extended attributes?

[FUJITA Tomonori]

On Sat, 3 May 2008 16:23:56 +1000
"ronnie sahlberg" <ronniesahlberg at gmail.com> wrote:

> Cool.
> 
> How far is you ssc?  can one do basic i/o with say mt with it?
> 
> While SSC is very different,
> in MMC I would like to be able to store things like a barcode,
> serialnumber, and other MAM and MAM-like data  attached to the backing
> store file.
> I want it to be stored in a was so that this data is "attached" to the
> file that contains the actual image of the media.
> I dont want to use separate files to store the metadata, so extended
> attributes would be a nice way to associate the metadata with the
> actual data.
> 
> In MMC I think it would also have value if the actual file itself,
> reading all data from position 0 to the end of file would be an
> identical image of the data
> of the disk itself.  I.e. the file content IS the actual .ISO of the
> disk.  Which would allow such files holding a STGT MMC backingstore
> to be mountable as
> a ISO9660 filesystem through loopback   and also be immediately
> compatible and work with the myriad of "Virtual/Phantom DVD Drive"
> applications
> and drivers on other systems.
> This compatibility would fail for me if I store metadata at the
> beginning of the file.
> (Yeah, you can mount the file as an .ISO   but you have to strip off
> the first xMByte of the file first :-(   compared to "the file is just
> a normal .ISO image so its compatible with anything under the sun (but
> it also has some invisible extra metadata stored at the side)". )

As you said, we need to consider both the pros and cons of using
metadata. People are happy to give up the compatibily and use virtual
disk images (like QCOW, VMDK, and VHD) for snapshot. I think that just
for something trivial like serial number is not a good idea. Does the
metadata give something huge for mmc and ssc (like snapshot for sbc)?