Hi everbody!
I have IDS 7.31UD10 on Solaris 9 SPARC, size of my databse > 2Gb.
I want to make backup by ontape + pipe.
What value of TAPEBLK I must to define in ONCONFIG file?

You need to check your tape drive reference manual to see what it can handle.
Range of values
Values greater than pagesize/1024

The database server does not check the tape device when you specify the block size. Verify that the TAPEBLK tape device can read the block size that you specify. If not, you might not able to read from the tape

I want to do backup on disk.

The above should still apply. Set it to your pagesize / 1024. For example, if your using a 2k pagesize:

2048 / 1024 = 2

So set it to 2 or more.

I solved my problem by TAPEBLK=8