DDS4 device file to write to a 90m

[Lisa Mauer]

Yes, I posted this twice - once in the storage forum and once here - hoping someone has found a workable solution to this question :) Between the sys admin gurus and the storage gurus, wondering if anyone has gotten this to work....
***************************
Don't ask why - but we need to write a tape from a server that has a DDS4, and we need to write to a 90m tape... Anyone know of a way to create a device file using a lower density to get this to work? Realizing this isn't supported, but thought maybe someone found a back door.....
Thanks!

[A. Clay Stephenson]

You best "workaround" is to go out on the the used-equipment market and find an old low-density drive. I keep an old DDS2 drive that I always use in uncompressed mode to create tapes that anyone read. You should be able to find a drive for almost nothing.

[Tom Danzig]

Try:

mksf -C tape -H 3/2/0.8.0.0.3.0.0 -b 19 -c 1 /dev/rmt/0m_DDS1

Using this device file to write to the tape drive at 0m should write it in DDS1 format.

[Tom Danzig]

NOTE: Adjust hardware path in above as appropriate

==========================
Try:

mksf -C tape -H 3/2/0.8.0.0.3.0.0 -b 19 -c 1 /dev/rmt/0m_DDS1

Using this device file to write to the tape drive at 0m should write it in DDS1 format.

[S.K. Chan]

I'm not very sure about this but I can vaguely recall that I've done this before .. ie creating a device file that has a lower density for a higher density tape drive. Take a look at the man pages for "mksf" (the -b option can be specified along with the needed tape density). In you case try ..
# mksf -H -d stape -b DDS2 /dev/rmt/mydrive
You can then use /dev/rmt/mydrive "as if" it's a DDS2 drive.
Like I said, I can't confirm 100% if it'll work.

[Zeev Schultz]

Why not to create with mksf something like
/dev/rmt/cXtYdZDDS1?
use flag "-b DDS1",like this:
mksf -H 4.2.0 -b DDS1 (and your tape is on 4.2.0)

Regards
Zeev

[Kelli Ward]

FYI -
The mksf man page says S.K. Chan's suggestion should work.
I'd give it a try. man mksf
It has a couple of entries for -b, the entry cross referenced to the driver option (-d) has a bits per inch entry for -b to set the tape density.

Best of luck to ya. :)
Kel

[Lisa Mauer]

Thanks for all the responses! I tried Tom's suggestion and it didn't work, I get
could not open output file /dev/rmt/0m_90DDS1
crud....
In S.K 's suggestion you say to try and use it as a DDS2 - even though a 90 meter is DDS1 right? Or was that a typo and should have been DDS1?
I'll pretty much try anything so I will test the next one and let you know.
Thanks again!

[Lisa Mauer]

Well I tried them all including changing the DDS2 to a DDS1 and nothing.... Thanks anyway! I thought there was a way around everything :)

I think we will end up using a DDS3 remotely on another server. Oh well :)

Thanks again!

[Shannon Petry]

Let me see if I can learn ya something ;)

The reason this does not work has absolutely NOTHING to do with Software and/or Drivers, but rather hardware.

Is there a way to put a 10K RPM LVD SCSI on a SCSI-1 buss and make it work? Even if you change drivers?

If you answere no to these, then you should understand completely that the technologies in the devices cause the problem, not the driver.

Understand that the biggest confusion about this comes from the fact that DDS4 can read DDS1/DDS2/DDS3 format tapes. However, the grain at which a DDS4 writes is very very small. Compare this:
DDS2 150M tape Capacity 4-8GB
DDS4 150M tape Capacity 25-40GB

The tapes are not "that" much different, but the read/write heads are absolutely different.

In the simplest explenation, the DDS4 can write data to a DDS1, DDS2, and DDS3 tape. Howerver, it's write size is too small for a DDS1, DDS2, or DDS3 device to read. There is no possible way to take this micro fine write head any larger, so there is absolutely no way of "making it work".

Hope this helps.

Sincerely,
Shannon

[Kelli Ward]

Sorry 'bout that guys.
Silly me, thinking that an option like
-b "bits per inch" would format the write size so that a higher compression drive could write so that a lower compression drive could read from it.
Thanks for the learnin'Shannon
Didn't hurt too much.
I guess the -b bits per inch should really stand for:

Big
oPtion
Imposter

Kel :)

[Bill Hassell]

The DDS format is VERY different than reel-to-reel tapes used in the 60's (and still in use today). In those tapes, the magnetic bits were written with a multitrack head and the bits are vertically aligned. Thus, electronics could create a density of 200, 555, 800, 1600, etc). But DDS uses a helical scanning system which is much more difficult to make backwards compatible. This is why there is no density setting for modern tape drives. The density option is simply a switch for compression on/off. DDS drives announce the type of tape (DAT, DDS1, DDS2, DDS3, DDS4) with a media recognition system. That is why putting a DDS4 tape into a DDS2 drive doesn't work--it is ejected. The media is quite different between DDS1 and DDS4 and the higher density media can easily wrap around the mechanism causing a very expensive service call.

DAT (which is not DDS) is a 60meter tape with a very high error level, thus not suitable for digital data. Audio data can be interpreted (just like audio CDs) when the data stream is full of errors. DDS standards don't allow this low quality tape which is why 60meter tapes (and tapes without media recognition) are automatically treated as read-only.

There have always been issues going backwards with DDS tapes and the wider the gap (ie, DDS4->DDS2 versus DDS3->DDS2), the more likely there will be compatibility issues. Since DDS2 is so old, you can usually pickup used DDS2 tape drives for $100 or so and that would be the best compatibility solution.