LTO Vs. SDLT In A Tivoli Storage Manager Environment
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While studies produced by the manufacturers of Super Digital Linear Tape (SDLT) and Linear Tape Open (LTO) suggest a wide disparity between the performance of the two, our testing indicates the opposite: these two technologies perform in similar fashion in a Tivoli Storage Manager environment. This is not surprising as both technologies are perhaps more similar than they are different.
Other studies conducted on these technologies strayed from the real world into the purely hypothetical. Therefore, depending on the data streams manufactured for the test, one or the other technology can be shown to prevail. We chose to provide you with information about the environment you are most likely to see as users of TSM.
Overall, our testing suggests that LTO out performs SDLT by about 10% in normal day-to-day TSM operations. These operations include backup stgpool, storage pool migration and move data operations. For tape-to-tape operations, LTO appears to hold a larger edge. This difference may become apparent during tape reclamation operations. Again, however, the differences are not great enough to warrant a decision based on entirely on performance.
When conducting tests of this nature one easily becomes distracted with other aspects of the environment. While our original goal was to test tape drive performance, we strayed into the larger world of overall TSM I/O performance. Specifically, our first set of tests yielded a surprise: single stream backup stgpool was as fast as the aggregate of two streams. This suggested a performance bottleneck elsewhere in the system. Indeed, the RAID5 configuration used in the first test appears to be a bottleneck.
Subsequently, we tested a number of other disk configurations. Our results are not surprising: JBOD (just a bunch of disks) is faster than RAID5. Significant? Yes, in some tests. However, does the speed of JBOD outweigh the security of RAID5 or the cost of RAID0? We'll let the reader decide. In our testing, the overall performance improvement using JBOD vs. RAID5 is about 20%. For most sites, this may result in 30-60 minutes of reduced processing time. However, in very large sites the savings may be much greater.