TSM 6.x NDMP problems
We recently were implementing a new TSM farm, based on TSM 6.1.
Since we are also using a NAS system, we were also testing the NDMP functions of TSM6 against our NAS device. We previously were using TSM5.5 which worked fine so we expected it to work just as fine in TSM6.1
Unfortunately it didn’t. We opened a PMR with IBM to investigate this problem, but they quickly pointed to the NAS vendor. IBM/TSM support said the NDMP code was not changed from TSM5.5 to TSM6.1, and TSM uses an NDMP API to perform the NDMP functions agains a NAS device. So we also opened a ticket with the NAS vendor support dept. We did some traces on TSM5.5, TSM6.1, and the NAS device. All commands and responses were like expected, and there seemed to be nothing wrong. We send the ticket back to IBM/TSM because the TSM version was the only change made. The NDMP backup was still working perfectly with TSM5.5, and not a single change was made on the NAS device. So the obvious cause had to be TSM.
After some more investigation IBM/TSM support came out with a probable cause (not confirmed yet) being memory management changes in TSM6.1. In TSM5, memory is still allocated if required bytes is zero, while in TSM6 no memory is allocated and null is returned when the required bytes is zero. The “show nasd” command will not work if zero is the value of SCSI info in TSM6. All commands in TSM to define paths to the tape drives the NAS device sees, will fail as well.
This problem applies to all TSM6 releases currently out there. An official APAR is not yet opened, because we will be running some additional tests with a special purpose built TSM server to further diagnose with greater detail. I will update this post when these tests are done and the APAR is filed.
I do have to note though that although IBM and the NAS (HDS) vendor are competitors in the NAS arena, they did work together nicely to resolve this issue for the customer. Although this should always be the case in the interest of the customer, I have had a case or two when the vendors wouldn’t cooperate and the customer was left in the dark. So to me, IBM and HDS deserve a compliment for this.
