CRC question, Informix 6.0

Hello, I have been asked to make comparisions of Informix's backup utilities from version 4.0, 5.0, and 6.0. While researching this, I found a small paragraph in the "INFORMIX-OnLine Dynamic Server, Archive and Backup Guide 6.0" (p. 2-28) that mentions the option of adding a CRC qualifier at the end of each save set block during archives and backups (ON-Archive). My question is, does INFORMIX, 1. calculate the CRC and write it to the tape, or 2. calculate the CRC, then back up the tape and re-read the save set, calculate a comparison CRC, compare the two CRCs, and then when a comparison is successful, write the CRC to the tape (or something like that)? The difference in the two methods being, the first method doesn't actually verify that the data on the tape is readable, while the second method verifies that the data on the tape is readable and valid. If the second method is the one used, it reduces the possibility of having a bad backup or archive, caused by things like static, where the software thinks everything went okay, but when you try to use the tape, it's useless. Thanks. -- Laura Schouweiler Unix Integration Services Phone: (515) 254-3074 11033 Aurora Ave., Des Moines, IA 50322 laura@uis.com