cd reader external

[Rick Stevens]

On 09/19/2012 04:35 PM, Mikkel L. Ellertson uttered this comment:
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> On 09/19/2012 04:46 PM, Rick Stevens wrote:
>> On 09/19/2012 12:16 PM, Mikkel L. Ellertson uttered this comment:
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>>> On 09/19/2012 11:50 AM, Rick Stevens wrote:
>>>> On 09/19/2012 05:18 AM, Patrick Dupre uttered this comment:
>>>>> Hello,
>>>>>
>>>>> Can I use (mount?) a cd reader from another computer?
>>>>> Both computers are on internet, In aother words can I do a
>>>>> mount 122.255.988.10:/dev/cdrom or similar?
>>>>
>>>> Not really. You can ssh to the remote box, mount the media on the
>>>> remote box, then export that mount from the remote box via NFS or
>>> CIFS.
>>>>
>>>> On your local box, you'd mount the export from the remote box
>>> using the
>>>> appropriate mechanism (NFS or CIFS).
>>> I wounder if ISCSI would let you do this?
>>
>> It would if the remote device was an iSCSI target and everything had
>> been set up cleanly. Remember that iSCSI only offers up raw block
>> devices. The mount of the remote device would have to know what
>> filesystem type the remote device was. iSCSI can be confusing.
> I was thinking the local system would take care of mounting the
> device using SCSI commands over the network to access it as if it
> were attached to the local machine. But I may be misunderstanding
> what iSCSI does. I have not looked into it in depth.

Essentially that's it. The machine with the physical hardware offers
it up (at this point, it's called the "iSCSI target"), but it appears
as just a raw block device--there's no filesystem overlaid on it.

Your local machine (the "iSCSI initiator) would have to know what the
target was to mount it with the appropriate filesystem applied.

> It sounds like you know a lot more then I do about it. Would the
> device ID from the remote device show that it is a CD/DVD drive?
> Could the drive be handled the same way as an USB CD/DVD drive? But
> using iSCSI instead of USB as the communication channel to the
> drive? The same upper level drivers used for almost all CD/DVD
> drives, with only the low level drivers changed to use iSCSI instead
> of low level SCSI/ATA/USB to communicate with the drive?
>
> What I am thinking of is that all the remote system would do is
> handle the communications between the network and the physical
> device driver, just like it handles communication between the
> physical device driver and the high level SCSI drivers when you
> access the device locally. Then on the local machine, the ISCSI
> drivers would take the place of the physical device driver, and the
> rest would be handled as if it were a local drive. The remote
> machine would never have to know what file system is involved. It
> would just pass commands and data between the network and the
> device. (Start read at track x, sector y, and return z blocks of
> data.) The remote machine would never mount the file system.

You handle the target like any other raw block device. If you want
to apply a filesystem you can. If you want to just read N raw blocks,
that's fine, too. I have, in the past, exported storage farm LUNs as
iSCSI targets to iSCSI initiators running Ingress or Oracle databases
and those initiators use the LUN as the datastore. There's no filesystem
per se, just a raw device that Oracle uses as the storage.

As I said before, iSCSI can be confusing (targets, initiators, sessions,
lions, tigers, bears, oh yy!) but once you're into it, it's
decipherable. Just keep in mind that the devices passed around (targets)
are raw block devices and are treated as such by the initiators.

-- 
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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
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