dds3 tape backup restore on to system with dds4 drive

[Peter Gillis]

Hi,
Hpux 11.00.

Hoping for some quick help here...I have a dds3 tape that has a backup on it. I now need to restore the contents of this tape on to a machine that only has a dds4 tape drive.

Anyone got any suggestions on how I might accomplish this? Do I need to create some sort of special dev file?

Thanks for your help..
Maria

[James Murtagh · Accepted solution]

Hi Maria,

Going forward you should be fine, i.e. dd3 -> dds4. No special configuration needed. Note if you created a backup on dds4 you couldn't restore it from a dds3 drive.

Regards,

James.

[Bill Hassell]

The DDS formats are upward compatible, so a lower level tape can be read on the same or higher level tape drive. No special device file is needed as the readability is resolved within the tape drive.

[steven Burgess_2]

Hi Maria

you will be ok with a dds3 tape and a dds4 drive. if vice versa you would have a problem

check ioscan for your drive path

ioscan -fnC tape

Check you have a device file for the drive

ll /dev/rmt/#m

If not create one with

insf -H

HTH

Steve

[Michael Tully]

Hi Maria,

I have the same problem here, where I have all sort of different drives. A DDS4 will read 150, 125 and 120 meter tapes in standard format. Using 90m tapes you may have problem.

If you had a tapes that was created on a DD4 drive and you wanted to use on a DDS3 later, you would then need to create a special device which changes the bytes per inch.

Regards
Michael
"When I have trouble spelling, it's called fat finger syndrome"

[Jeff Schussele]

Well, I agree with everyone's main point - upward read compatibility.

But I'm still smarting from being dinged on a DDS-format comapatiblity question. I always thought that IF one writes a DDSX format(length) tape on a DDSX+1 format drive that you forfeit that downward compatibilty. I.E. the BPI would be unreadable by the older drive. But, I was told that the drive senses the tape format & adjust the BPI.

Bill - can you confirm or refute?

Thx,
Jeff

[Bill Hassell]

The DDS format is not just a simple BPI change. DDS drives are like video tapes. The data is recorded at an angle across the tape and the data records are interleaved along error correction and other control codes.

Although each DDS format supports a longer tape, the characteristics of the tape (magnetic properties, thickness, stiffness, etc) are different. So putting a DDS4 tape into a DDS2 drive will never work. The DDS2 tape drive would see the media recognition code at the beginning of the tape and immedately ejects the tape. This keeps longer tapes from tanlging in the very tight tolerance tape path.

Device files for modern tape drives no longer have a BPI setting. Instead, there is a bit for best density which enables compression for writing. The tape drive senses the data format for reading and handles compression automatcally. So nothing special is needed to read compressed or uncompressed data from the same or lower level DDS tapes.

[Michael Tully]

Thanks Bill,

Then why is it that we can write tapes onto say DLT8000's in virtual DLT7000 mode? This can also be done on some DDS tapes as well. The man page of 'mksf' makes mention of these.

Regards
Michael
Michael
"When I have trouble spelling, it's called fat finger syndrome"

[Peter Gillis]

Thank you everyone,restore worked fine. But< I am now curious. Looks like I can use dds3 tapes for backups on dds4 drives, for that though I would need special dev files...right?

So how do I know which special dev files to load? I know these are probably really basic questions, but am the only ux admin here and learning on the job. Amazed at how much I have learnt using this forum. Thanks for taking the time.

Maria.

[Jeff Schussele]

Thanks Bill.

Forgive me for the dolt I am....But I still don't think I have the answer to my question.
So you're saying that if one wites a DDS2 tape in a DDS4 drive - another DDS2 drive can read it?

Thx,
Jeff

[Jeff Schussele]

Hi (again) Maria,

No apologies necessary, my dear.
But you gotta just LOVE this place - huh?
Where else can you be exposed to, this directly, the BEST talent in any OS arena?!?!?
Heck - this guy we're interacting with is not only one of the BEST HP-UX talents around - he's also probably the most hairless. =~))

Cheers,
Jeff

[Bill Hassell]

That's a complicated question so don't feel too bad about not knowing what the outcome will be. Here are the (complicated) details:

http://www.hp.com/products1/storage/products/storagemedia/tape_dds/compatibility.html

The newer drives do sense the type of tape and will adjust recording method where possible. But not all lower level tapes can be written by a higher level drive. The second chart shows the blank spots for compatibility. The DDS4 drive can write to DDS3 and DDS2 tapes and those tapes should be readable on DDS3 and DDS2 drives respectively (based on the chart). I would play it safe and test the backward write capability. As the chart shows, DDS4 is not compatible with DDS1 media.

[Michael Tully]

hi Maria,

Using a tape that was created on a DDS3 drive should have no problems being read on a DDS4. No special device files are required.
Using a tape that was created on a DDS4 drive will not be read on a DDS3 drive unless you create a special device for the DDS4 drive prior to cutting the tape.

For memory this is how to create the device file e.g. hardware address.

# mksf -C tape -H 0/12.3.0 -b DDS3 -c 1 /dev/rmt/myspecialdevicename

The man page of 'mksf' contains the standard types that can get created. As far as creating a DDS2 device for a DDS4 drive, sure you can create the device, but as far as getting it to work ... ??

Regards
Michael
"When I have trouble spelling, it's called fat finger syndrome"

[Peter Gillis]

Thanks Michael, Bill, Jeff, and everyone else. So good to hear from people enjoying sharing valuable info.
Thanks.
Maria.

[Jeff Schussele]

Hi Maria,

This is *why* we're here.
To answer your question...
You can use that DDS3 tape in that DDS4 drive & rely upon it.
And according to that chart - all DDS3 drves will read it.

Cheers,
Jeff