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LTAPEBLK influence on backup size to disk

  • 1.  LTAPEBLK influence on backup size to disk

    Posted 19 days ago
    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 204800000

    When 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?











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    Luis Marques
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  • 2.  RE: LTAPEBLK influence on backup size to disk

    Posted 19 days ago
    Every backup will always be enclosed in between a pair of header and trailer blocks, each size [L]TAPEBLK.

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    Andreas Legner
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  • 3.  RE: LTAPEBLK influence on backup size to disk

    Posted 16 days ago
    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 ?




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    Luis Marques
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