DAT 20/40 drive occasionally overflows tape

[Bob_Peitzke]

On this W2K server with an internal DAT 20/40 tape drive, running BE 9.1, full backup jobs normally write about 18 GB. Occasionally I get a job that ejects the tape at only ~ 15.5 GB written. While the drive is a 20/40 DAT, the tapes we've been using in it are DDS-3. (I will suggest we start using DDS-4 tapes.)

I'm wondering whether I should adjust the tape drive's configuration parameters to optimize tape usage. Currently its settings are
- Block size = 8K
- Buffer size = 32K
- Buffer count = 10
- High water count = 7
All options for "single block mode" and "SCSI pass-through mode" are unchecked.

Advice?

TIA

Bob Peitzke
IT Manager
Colony Advisors, LLC

[Ken_Putnam]

Your current problem is most likely due to the DDS-3 media. 15GB on a DDS-3 is about 1.25:1, right in the range that I use as a rule of thumb (1.3:1)

If the device will support it, you could try playing around with the Block/Buffer sizes.

Try working up to a block size of 32K in increments of 8K, and make your buffer twice the block size. Buffer Count = 10 should be good. Larger Block Size might not affect the total bytes to tape much, but it should speed up the transfer rate noticeably if not significantly.

[Deepali_Badave]

Hello,

You can also refer the following technote:

http://support.veritas.com/docs/199542

NOTE : If we do not receive your reply within two business days, this post would be marked assumed answered and would be moved to answered questions pool.

[Bob_Peitzke]

Thanks, Ken. I will try adjusting the block size as you suggested.

I wonder if there is a chart anywhere showing optimal block sizes & buffer sizes for the various DAT drives.

Happy New Year!

- Bob Peitzke