I upgraded to SCO OpenServer 5 and BackupEDGE 1.1, and can't use block sizes over 256.

Keywords

edge BackupEDGE OpenServer OSR5 tape block factor

Release

BackupEDGE for SCO OpenServer 5 Release 01.01.0x

Problem

Under Unix 3.2v4.2 I could use large block factors. I recently upgraded to SCO OpenServer 5 and BackupEDGE 1.1. Now I can't use block factors above 256.

Solution

SCO OpenServer 5 defaults to "Variable" Block Mode with many tape drives, especially DAT/DDS drives. In variable block mode the maximum block factor is controlled by the CTBUFSIZE kernel parameter. Its default value of 128 [1k] blocks means the maximum available BackupEDGE block factor is 256. Remember that BackupEDGE measures its blocking factor in 512-byte blocks, so the maximum blocking factor will always be twice CTBUFSIZE.

To increase the BackupEDGE block factor above 256 it is first necessary to reconfigure the CTBUFSIZE kernel paramater to [desired_block_size] /2. For instance, to use a BackupEDGE block size of 768 you must set CTBUFSIZE to 384 or higher, then relink the kernel and reboot.

	  NOTE 1:  The OpenServer 5 configuration program will display
                   warnings if you attempt to set CTBUFSIZE above 256.
                   These may be safely ignored.

          NOTE 2:  Make ABSOLUTELY SURE you perform a MASTER BACKUP
                   and BIT-LEVEL Verification before trusting your
                   data to the new block size.  Some tape drives
                   may fail to return errors at larger block sizes,
                   but in fact incorrect data is written.  The
                   BIT-LEVEL Verify will ensure that you can use
                   large block factors safely.

          NOTE 3:  To use a BackupEDGE block factor of 1024 or higher
                   it will be necessary to increase the kernel
                   parameter SHMMAX beyond its default of 524288, then
                   relink and reboot.

          NOTE 4:  BackupEDGE double buffering does an excellent job
                   of keeping the tape drive queue full in most
                   instances.  It is rare that using a block factor
                   above 256 along with double buffering will result in
                   significantly increased backup speeds on most systems.

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