I need to backup my database but the files are very large and the TAR command will not let me. I searched aids and found that I could do something with the mknod, COMPRESS and TAR command using them together. I appreciate your help.
What do you mean it will not "let" you, what happens when you try?
What system are you on? tar often has compression built in, if you use the appropriate option, i.e. -z for gzip, -j for bzip2: tar -zcf file.tar.gz input files ...
What sort of data is it? Text compresses very well, other data depends on how structured it is.
System AIX 7.1
The message : file too large
Type of date: Oracle datafiles
We have not enought space on disk and we can't grow it at this moment.
Use a pipe to a compression program
tar cf - files ... | gzip -c >file.tar.gz
We need to copy de files compressed to a tape. I don't know if the space on disk is enought for the compression process thats what I talk about MKNOD command. Using pipes the files are compressed and sent to the tape without left temporal files in server.
mknod provides device nodes - certainly not useful here.
It seems this AIX tar cannot open files bigger than 2GB?
Then upgrade/patch it. If not possible, install GNU tar (gtar).
Is it saying it can't create that large a file, or it can't open that large a file?
You can avoid temp files:
tar -cf - /path/to/files | gzip | dd of=/path/to/rewinding-tape-device
There is probably a more proper way to use tapes on AIX.
Corona688 your sugestion works, but when I restore de information from tape with the command "dd if=/Tape_Device of=File_Name", it starts with some characters that corrupts the file, it is caused by the TAR command. How can I supress it? Also is a problem when using dd command to send de file to the tape because it most be recovered giving a filename.
If you followed Corona688's suggestions, you used "tar" then "gzip" on the files before using "dd" to write the data to tape.
What is your exact sequence of commands to retrieve the data?
The data is compressed, you need to pass it through gunzip before tar can understand it again.
dd if=/path/to/rewindingtapedevice | gunzip | tar -tf -
That will just list files. Change -tf into -xf or -xvf once you're sure it's finding the files.
Again, there is probably a better way to use tapes on AIX specifically, but that's beyond my knowledge, this is a generic UNIX fashion.
Thaks Corona688. I appreciate your help.