backward compatibility of DDS drives

[Ken Scharpell]

Hi all,

I read on another question that you cant read or write DDS1 and DDS2 format tapes in a DDS3 drive. Is this true ?

[Evert Jan van Ramselaar]

DDS is backwards compatible. So you can use DDS1 and DDS2 tapes in a DDS3 drive. Just not the other way around.

[Stefan Farrelly · Accepted solution]

All DDS drives are supposed to be backward compatible, ie. you can read a DDS1 or DDS2 tape in a DDS3 drive no problem.

If, however, you write a tape in a DDS3 drive you may not be able to even insert it into a DDS1 or DDS2 drive if the tape is too long, ie. DDS2 drives can take up to 120m tapes (not the 125m tapes a DDS3 drive can handle) or a DDS1 drive can only handle up to 90m tapes (not 120m or 125m).

But, if you have the right length tape, eg. a 60m tape, in a DDS3 drive then yes you can write it in DDS1 or DDS2 format so that you can now read it in a DDS1 drive. You need to create a special device file to write it in this format though;

mksf -v -H -b DDS2 -a -c

This will create a new device file which if you use it will write your tape in DDS2 compressed format. Leave off the -c if you want it in noncompressed format - which for a DDS1 drive you may need as really old DDS1 drives have no compression (DCL drives as opposed to DCLZ compressed DDS1 drives)

This allows you full forward and backward compatibility between new and old DDS drives.

[Ken Scharpell]

Thanks Stefan,

If im having trouble reading an old DDS1 (not sure if compressed or not) tape in a DDS3 drive should I also use the mksf command to create a new device file for a DDS1 (compressed or not) drive and expect it to now read aok ?

[Peggy Fong]

Just wanted to apologize for the confusion I introduced on that other thread regarding backward compatibility. My 60meter tapes were dat tapes...and since newer tape drives had problems with them we just didn't pursue getting the data off. I included a link to a matrix that shows the compatibility of tapes to tape drives which does show the backward capability.
Again, sorry for the misinformation...
Regards,
Peggy

[Stefan Farrelly]

Hi Ken,

Yes, I would expect it to work if you have a DDS1 written tape and are having trouble reading it on a DDS3 drive by using the mksf command to create a /dev/rmt/XX file as type DDS1. This tells the driver to access it as if it were on a DDS1 drive, not DDS3, it should work fine.

[Carlos Fernandez Riera]

DDS -> Digital data Storage
MRS -> Media recognition system
DAT -> Digital Audio Tape

All media after DDS2 is DDS-MRS, this is .. recogniced by the drives...

Oldest tape are wrote in 512 bytes Physical block. Newer DDS (2,3,4) write in 1024 byte Pysical blocks.


All DAT-MRS drives (DDS2,3,4) can identify what type of tape is inserted and the use the correct format. This is the true sense of BEST devices... write in best format available. DDS2 are 120m 4 GB, and DDS3 is 125m 12GB (native). You can not write 7 GB ( native) in DDS2 tape in a DDS3 drive, what means that the format of writing is diferent physicaly.


I am not absolute sure if DAT4 drive accepts 60m DDS1 or DAT1.


I guess that older tapes in 512b physical block can be read automaticaly in DDS2,3,4 drives but if is not true, you can create a spacial file . See man mksf. In a recent response http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x171172106351d5118fef0090279cd0f9,00.html i have write how to do this..,, and that response is Rabbit'd .. so....


Regards.