DDS4 Drive Questions

[Sameer_Nirmal]

Hi Guys,
I have 4 DDS4 DAT drives housed in 5300 Tape/DVD array connected to rp7410 server with HP-UX 11.11 ( v1)

I want to copy some data from the server to one of the DDS4 drives so that i can copy it to another server with DDS3 drive ( both server are at different locations and not connected through network ).

One way is to create a device file for DDS3 tape density with mksf command. But I didn't find the attribute for DDS3 tpi in the man page of mksf. Which one I should use?

Secondaly I have doubt about media compatibility as well. Lets assure that the device file is created for DDS3 tpi, can I make use of DDS4 media for taking data backups with DDS4 drive and DDS3 tpi ? and would the same media could get read in the DDS3 drive?

Another issue is with one of the DAT drives which only shows BEST, DDS tpi device files in ioscan command and not /dev/rmt/13m or 13mn device files? why is it so?
I checked up connections, terminations etc. and could able to use the drive with those device files created. I tried insf -e as well as system reboot once , but it didn't work.
It is not creating the /dev/rmt/13m or 13mn files..

Pls advise and clarify....
Your feedback would be appretiated

Thanks
Sameer

[Victor Fridyev]

Hi,

I never had problems with copying between different DDS devices if the media can be used in the lowest device version. Put 120M tape into DDS4 drive and everything should work.
Re nunmering, you can do nothing with this: the computer remembers that once there was a tape drive with another SCSI ID connected. If you want to use rmt0 drives only, create appropriate links or mknod with the same attributes as for rmt1

HTH

[Antoniov.]

I'm with Victor on that.
Use lowest density tape to carry data. Best choice DDS2 90/120M.
However I met some trouble between differents device (I'm not using unix but DDS are the same)

Have a great day
Antonio Vigliotti

[Antoniov.]

Hi Sameer,
to best clarity, when I carry my software form a DDS device to another I always make two copies on 2 different tapes and I've the clean tape.

Antonio Vigliotti

[Bill Hassell · Accepted solution]

DDS tape drive formats are not just a higher density or longer tape. The recording method is unique for each higher level and the tape characteristics (thickness of the tape, magnetic properties) are different. There is no possible way to record a DDS4 tape so it is compatible with a DDS3 tape drive. First, the DDS3 drive will reject the DDS4 tape - it's not compatible. This is true for all previous DDS drives except very early DDS1 drives. The reason to reject the tape on earlier drives is that longer (and thinner) tapes would wrap around the tape transport and jam the unit. Such jams usually require complete replacement of the drive.

Now a higher level DDS drive (ie, DDS4) can write a lower level tape (ie, DDS3 or DDS2). The reverse (DDS3 writing DDS4 tape) is not possible. The drive will recognize the type of tape using the MTRS holes in the leader of the tape. Most important, the density (BEST, etc) have nothing to do with DDS2, DDS3, DDS4. The BEST density refers to hardware compression. Unlike reel to reel tape drives (you can see them in computer museums) where there were several densities like 200, 555, 800, 1600, etc) DDS drives always record in one format for each drive type). So density is a leftover term from the past--it means compressed or not compressed.

So you use the same device file for writing a DDS3 taoe as you would for a DDS4 tape. I don't know anyone that uses the non-compressed device files. Just use the shortest names (saves typing) such as 0m or 0mn or 0mnb. If you use the lssf program to decode the device file settings, you'll see that these names are all BEST density which means compressed.

AS far as the missing device files, you can easily re-create them using mknod. First, sort the device file names with:

# cd /dev/rmt
# ll | sort -k6
crw-rw-rw- 2 bin bin 205 0x023000 May 27 21:05 0m
crw-rw-rw- 2 bin bin 205 0x023000 May 27 21:05 c2t3d0BEST
crw-rw-rw- 1 bin bin 205 0x023001 Oct 9 2003 c2t3d0DDS
crw-rw-rw- 2 bin bin 205 0x023040 Aug 10 15:48 0mn
crw-rw-rw- 2 bin bin 205 0x023040 Aug 10 15:48 c2t3d0BESTn
crw-rw-rw- 1 bin bin 205 0x023041 Oct 9 2003 c2t3d0DDSn
crw-rw-rw- 2 bin bin 205 0x023080 Oct 9 2003 0mb
crw-rw-rw- 2 bin bin 205 0x023080 Oct 9 2003 c2t3d0BESTb
crw-rw-rw- 1 bin bin 205 0x023081 Oct 9 2003 c2t3d0DDSb
crw-rw-rw- 2 bin bin 205 0x0230c0 Oct 9 2003 0mnb
crw-rw-rw- 2 bin bin 205 0x0230c0 Oct 9 2003 c2t3d0BESTnb
crw-rw-rw- 1 bin bin 205 0x0230c1 Oct 9 2003 c2t3d0DDSnb

Now you can see that devicefile 0m and c2t3d0BEST are identical. If I were to remove 0m, I could replace it with:

# cd /dev/rmt
# mknod 0m c 205 0x023000

So re-create 13m and 13mn the same way. Devicefiles have only 3 features: the major number (205 in the above example) which is the driver number, the minor number which ties the devicefile to the hardware channel, and the type (c = character) of access.

[Sameer_Nirmal]

Thanks all for your reply guys.

Bill, I do agree with your feedback. Actually I had same thing in my mind about using DDS media. I will be trying to use DDS3 tape with DDS4 drive and let you know
Actually the drive detects itself the media format and write or read accordingly, thats why we could get lower type media compatibility.

But , why do we need to create special device files using mksf?

For second issue, the /dev/rmt/13m device file is present. I guess i need to remove this file and create a link with BEST device file . These files are created to maintain compatibility with older naming convention, right?

Thanks
Sameer

[Tom Danzig]

Tou can create a DDS3 device file with the following if you like:


mksf -v -H -b DDS3 -n -a

[Tom Danzig]

You can create a DDS3 device file with the following if you like:


mksf -v -H -b DDS3 -n -a

[Bill Hassell]

I know of no reason that you need to create a BEST name other than something like SAM may default to a BEST name. Yes, the drive recognizes the media and changes the recording method to work with the older media. I would not recommend using more than 1 step though. A DDS4 drive writing to a DDS1 tape may not be as reliable. DDS2,3,4 drives will not write to non-MTRS tapes (such as DAT) although they will attempt to read the media. The defect count in DAT media is too high to be used in DDS drives.

mksf is just a front-end for mknod. AS you noticed in the ll listing, the minor numbers are the same for BEST and non-BEST device names. The last two digits of the minor number control the driver behavior (no rewind, compress, Berkeley or ATT behavior, etc) and after you use mksf, you still end up with a major + minor number, regardless of the name, and the minor number is all that counts for device features.

You could create a link but I wouldn't. Just use mknod to create the same numbers. You can rename (mv) tape device files to anything, or create your own with mknod. Again, major + minor define the device file's features. lssf will decode the values. But good sysadmin practices would imply using standard names (I never use the BEST devices because they require too much typing).

[Ted Buis]

You need to make sure that the scsi tape driver is in the kernel. If no tape drive was connected when the OS was installed, it often isn't there.

[Sameer_Nirmal]

Guys,
Pls clarify my one more doubt about DDS media . This time I am using Sun systems with DDS drives.

My client has taken a export backup of oracle with ufsdump on DDS4 drive with DDS3 media. I was told the size of the dmp file is around 10GB. He is trying to restore the same in another Sun machine with DDS3 drive, but couldn't as error says error reading the file ( Sense Key = Media error ). The same media was tried with DDS4 drive , it worked fine and the file could able to restore.
The media is HP 125M 24GB . Why is it so?

My understanding is media written on DDS4 drive can't be read in lower DDS version drive. Is it right?

I tried with Fujitusu DDS3 media on DDS4 drive , took ufsdump with 64MB file. Thereafter I could able to ufsrestore the same in the DDS3 drive. This has made my understanding as wrong!!!!

Pls clarify...

[Bill Hassell]

None of the DDS formats are backward compatible. DDS4 cannot be read on DDS1,2,or 3, and so on. In fact, if the DDS drive conforms to the industry standard for media recognition, putting the DDS4 tape into the DDS3 drive will fail--it will be rejected.

HOWEVER: If you use DDS3 media (tapes) in a DDS4 drive, it will NOT write DDS4 format, it will be DDS3 format. Same with DDS2 tapes put into a DDS4 drive.

[Sameer_Nirmal]

Hi Bill,

Your reply is appretiated..

Do you mean to say that a DDS3 media written on DDS4 drive would read on DDS3 drive ???

If yes, Why I couldn't able to read DDS3 media in DDS3 drive with 10GB file size??

Does the hardware compression ( default )of drives plays significant role for this compatibility?

Regards
Sam

[Sยภเl Kย๓คг]

Sameer
DDS3 tape written on a DDS4 drive will read on DDS3 tape drive.I didn't face any such problem in using so,still i am doing the same.Why can't check the DDS3 drive for any problems.
regards
SK

[Bill Hassell]

I only have experience with HP tape drives, so I can't speak for how the Fujitsu drives will work. Hardware compression is automatically sensed by the drive itself so you don't have to do anything special to read the tape. Does the error (Sense Key: Media error) occur at the very beginning of the tape or after some data has been read? The error seems to indicate that there is a bad spot on the tape, so I would clean both drives with a cleaning tape and use a different tape. The size of the backup will not affect the compatibility of the tape media.

[Sameer_Nirmal]

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