Ultrium 230 slow reads on variable block lengths

[David George]

We are using Ultrium 230 tapes to collect scientific data. The data are recorded by a vendor program with variable block lengths. When we read the data from the tape, performance is very slow -- a full minute for 50 MB.

We have one system running a 1/9 Autoloader under Windows NT4 and another running an external Surestore Ultrium 230 under Linux. Performance is similar on both systems.

It appears that perhaps the poor performance has something to do with delays in the drive firmware and the calls being used to read variable block lengths. While reading, actual tape movement is once every 10 or 20 seconds. This same performance has been demonstrated using a vendor's software (the vendor who wrote the software to write the tapes), it has been demonstrated using Windows NT ReadFile API calls, and it has been demonstrated using NovaStor's TapeCopy application.

I can write the same files to tape using default tape storage parameters and read the files back in about 3 seconds so the problem is not hardware. And the same files that take a minute to read are being written to tape in about 15 seconds.

I am hoping someone can steer me to correct SCSI commands or to mode initialization parameters. Would RecoverBufferedData work to simply dump the tape drive buffer to memory? It is not necessary to preserve the blocked structure physically on the tape and this includes EOF marks.

Thanks