Summary
This article describes how to verify that a tape drive supports large blocksizes (>32KB).
Symptoms
If the tape drive does not support the larger block size, the large data block will be broken down into smaller blocks by the drive during the write function. It will return a success status to the tape driver and application, suggesting there are no issues. However, the problem occurs during restores when the media attempts to position to the correct location on tape, which will fail.
Resolution
You should verify that a tape drive supports a block size greater than the default 32KB block size before making any application alterations that could impact the ability to restore valuable data.
To verify the large blocksize:
1. Check that the default tape read buffer is 32K. DPX requires using a variable read block size.
2. Put a new tape in the drive that you want to test.
3. Run the DPX tapedump utility from a command line prompt on the server connected to the tape drive.
- On UNIX, this tool is in BackEx/bin by default.
- On Windows, this tool is in backex\tools or Backup Express\tools by default.
- On NetWare, this tool is in SYS:backex\tools by default.
Use the following parameters to enter commands (variables appear in < >):
- tape<tape> (Use the tape device file. On Windows, this is tape\\.\tapeX where X is the number of the specific device you are testing)
- chbuf<block size> (If 128K, use 4 x 32 x 1024 = 131072)
- open rdwr
- rewind
- write a
- wfm 1
- rewind
- fsr 1
- fsr 1 (If this fails with "A tape access reached a filemark" message, 128K is supported because the tape drive did not write the buffer in smaller blocks)
- quit