LTAPEBLK influence on backup size to disk

Using IBM Informix Dynamic Server Version 12.10.FC13, on HP-UX ia64 , on a lab instance, I notice a strange behavior when using "ontape -a" to backup the logical logs to disk ( a file system directory visible by the informix instance ). Onconfig: LOGFILES 49 LOGSIZE 10000 DYNAMIC_LOGS 1 LOGBUFF 2048 LTAPEDEV /usr/informix/storage/volume33/backups/test_t LTAPEBLK 20480 LTAPESIZE 204800000When I do a "ontape -a" to do a backup of the logical logs to disk, I get the following type of files: -rw-rw---- 1 informix informix 62914560 Sep 11 13:18 ajtixs06_30_Log0000002657 -rw-rw---- 1 informix informix 62914560 Sep 11 13:18 ajtixs06_30_Log0000002658 -rw-rw---- 1 informix informix 62914560 Sep 11 13:19 ajtixs06_30_Log0000002659 So, 60 MB files for 10 MB logical logs. If I change LTAPEBLK to a smaller value, like 1024, with "ontape -a " I get the following files: -rw-rw---- 1 informix informix 12582912 Sep 4 09:33 ajtixs06_30_Log0000002654 -rw-rw---- 1 informix informix 12582912 Sep 4 09:33 ajtixs06_30_Log0000002655 12 MB files for 10 MB logical logs. If I once again change the LTAPEBLK to a smaller value, like 32 : -rw-rw---- 1 informix informix 10420224 Aug 12 17:02 ajtixs06_30_Log0000002629 -rw-rw---- 1 informix informix 10420224 Aug 12 17:02 ajtixs06_30_Log0000002630 10 MB files for 10 MB logical logs. I was under the impression that LTAPEBLK had no influence when doing backups to disk. But it seems to bloat the file sizes on disk. Is this the expected behavior? ------------------------------ Luis Marques ------------------------------ #Informix

Every backup will always be enclosed in between a pair of header and trailer blocks, each size [L]TAPEBLK. ------------------------------ Andreas Legner ------------------------------

Thank you for explanation Andreas. A couple more points then. - Do you know if the same padding blocks are also used with "onbar" backups? Online documentation says it ignores the LTAPEBLK value, but at the moment I have no way to check actual object sizes on a storage manager. - And in Informix 14.10 series, LTAPEBLK is also used on the secondary to set the size of 4 buffers that are used for logical log replay ( taken from the "IBM Informix 14.10: Replication Performance" presentation ). If it turns out that LTAPEBLK does bloat the size of the backup objects, in case of a promotion to primary or stand alone ? ------------------------------ Luis Marques ------------------------------