backup with dd fails with I/O error

[Stefan Herbig]

i run a backup with dd on an sap r/3 system against a orcale database. the media for backup is an dlt7000 tape drive. often i has seen the following error message from dd

xxxxx+0 records in
xxxxx+1 records out
I/O error

return code from dd is "2"
does anyone know something about problems like this, is it possible that system parameters doesen't have the right size ??

[melvyn burnard]

error 2 usually means there is no such file or directory.
I guess you need to confirm the if= and of= parameters are correctly set.

[Bill McNAMARA_1]

You should be able to identify this from the man on dd.
To verify your device files for the tape
use ioscan -fnkCtape
The device file for your database should be
your if not your of!!!!
Be carefull with dd.
The bs is not critical.

Do oracle not have their own backup software.
I'm not sure how great dd is, in particular
if you just want to recover one file..


Later,
Bill

[Marcel Boon]

Hi Stefan,

Can you give us the command you use ?

Marcel

[Stefan Herbig]

hi,

the dd command is generatet by sap-software, the parameters are set in a parameter file.
here 's the command

dd obs=64k bs=64k if=/oracle/C31/sapdata1/btabd_1/btabd.data1 of=/dev/rmt/c7t2d0BESTn

commands like the above where generated while the backup is running for each datafile of the database

[Marcel Boon]

Hi Stefan,

What is the output from ioscan -funC tape and dmesg ? Can you find somthing in /var/adm/syslog/syslog.log ?

Marcel

[John Palmer]

The xxxxx+1 message indicates that xxxxx whole and one 'partial block' has been written to the tape.

I've experimented with a large filesystem and a small tape and get exactly the same symptoms as you when dd reaches end of tape.

Regards,
John

[Stefan Herbig]

hi Bill,

i checked the output of ioscan -funC tape and it looks ok, i can see the device file, checking the syslog is a good idea but i couldn't find any error message concerning the tape drive or dd.

later stefan

[Stefan Herbig]

hi John,

good idea i looked for this but mostly the backup brakes soon after it has been startet. at this point of time the tape should not be at the end

later stefen

[Bill McNAMARA_1]

The n at the end of the device file means
no rewind so perhaps the tape is running out
of length?

Bill

[John Palmer]

Are you sure it's at the start of the tape. I would expect SAP to attempt to dd several volumes to the same tape.

If it's the first dd of a set, has the tape been reloaded or rewound?

Don't forget that using the no rewind device (as you do), you will have to specifically rewind/offline the tape with the 'mt' command or physically offline it after doing the backup otherwise the tape will remain positioned after the last file that you wrote.

Regards,
John

[Stefan Herbig]

Hi Bill, hi John,

i'm shure that the tape runs not on the end. the sap software is configured to rewind the tape first. after rewinding the tape administration information will be written on the tape with cpio and then the backup will begin. all datafiles are saved one after the other on the tape with no rewind (overwrite problem) if the tape will run to the end the backup should run a long time - so think i - hardware is ok - i've built in a new drive

thanks for helping me
stefan