HP C5683A Capacity

[Amit Freeman]

I have a SUN branded HP C5683A with the DIP switches set to Linux configuration. Operating environment is Redhat Linux 9. SCSI controller is an AHA-2940U using the AIC-7xxx module. I cannot, for the life of me, figure out why I cannot get at least 20GB per tape. I get approximately 17GB on each tape. Also, LT&T wont run to aid me in troubleshooting the drive. The error I get is "OC_Exception_c caught: Internal Error (oc_devicemap_linux.cpp, 534, Unable to find the SG device file).

Im probably doing something wrong, as this is my first experience with tape. I googled this for hours, and have come up with nothing useful. Can anyone either give me hints on getting ltt working, or shed some light on the storage capacity?

I shortly intend on writing out 20GB of zeroes to the tape drive to see if it will fit (and if it compresses). Any help would be appreciated

[Amit Freeman]

Incidentally, I am using both SONY 150m DDS4 tapes, and Seagate DDS4 tapes (I presume 150m as thats what its supposed to be to the best of my knowledge).

[CA843380 · Accepted solution]

Hi Amit,

Here is a link to some info on switch settings on the tape drive.

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?locale=en_US&taskId=120&prodSeriesId=63890&prodTypeId=12169&objectID=lpg51068

Native uncompressed capacity of the tape is 20GB so you are some way off this. Typically, loss of capacity below this figure is due to 2 possibilities:
1. You have both software (on host or backing up already compressed data such as jpegs and zip archives) and hardware compression enabled (in tape drive) and this can result in a small amount of data expansion, compression ratio less than 1.
You can use switches 1 and 2 on the bottom of the drive to enable/disable hardware compression irrespective of host control to explore this and see if you get different results with say hardware compression disabled, or always enabled. Hardware compression can be controlled on Linux/Unix systems by setting up the right sort of device file.
2. 2nd possible cause is loss of capacity due to the drive having problems writing and hence having to do rewrites to guarantee integrity of data written to tape, this wastes capacity. Without LTT up and running if is difficult to judge whether this might be the case.

I can't really help you with the LTT error, however, if does seem to be a device file problem?

Cheers,

Dave Dewar

[Amit Freeman]

Thank you for responding to my message. I actually got this issue resolved.... took a long time though. It was doing hardware compression (and the data set was mostly uncompressible). The LTT error I solved by compiling in SG support in the kernel.

Thing is, I did about 10 tapes of backups so far.... and it was working fine. Now suddenly it is doing the same thing as before... except I am disabling hardware compression with mt -f /dev/nst0 defcompression -1... and now its ignoring me. It still posts a line in /var/log/messages saying that compression default disabled.... but its not actually disabling. Any ideas as to why it suddenly stopped this behavior? When running L&TT, it used to say that compression was disabled... now it doesn't... and the DIP switches haven't been changed since.... any ideas?