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The answer fluctuates with time, file size, and a host of other variables that will ultimately affect (i.e., drop) the backup speed of the job being run. The table below shows the full path a backup takes from its source on a volume to its destination on a tape.
 All things considered when measuring backup throughput
What we do know is that the GB/hr. native throughput rate of LTO-1 is 52-56 GB/hr. We also know that most libraries either come with 8 or 12 drives (instead of the 10 mentioned). With 8 drives in a library, the native data transfer rate is 422 GB/hr. With 12 drives in the library, the native data transfer rate speeds up to 633 GB/hr. If there were no other considerations, you would be able to complete both your full and incremental backups in less than four hours every evening.
However, from this ideal, the data transfer rate drops due to various performance factors and setup factors. You say that this is a NAS solution on a SAN--so is this a NAS head on a SAN (meaning that the data is stored within the SAN and not on the NAS box per se)? If so, is the data being sent directly to the tape system using NDMP from the NAS to the Tape drive connected to it via Fibre Channel or is it being sent to the tape system via the VERITAS FlashBackup Server Free Agent across the SAN? Or is the data traversing the SAN through the NAS and over the Gigabit network to the tape system?
Each of these methods uses a different copy methodology and takes a different path.
The one that will provide the fastest backup speeds, is to run your NAS filer data as an NDMP backup directly to the tape cabinet, while simultaneously running two volume image or block level incremental backups from your Notes and Exchange volumes over your SAN to the same tape cabinet. You can do this as long as you've split the cabinet into multiple backup venues. A combination of VERITAS NetBackup 5.0 (or greater) backup options coupled with a Quantum PX-series tape cabinet (that can be divided into three) would do the trick.
*Divide the tape cabinet into three backup sections, each being controlled by a different methodology, as shown with the Prism setup for the Quantum PX series below.
Split system
*Use VERITAS' NetBackup 5.0 NDMP option to back up the NAS device directly to the tape cabinet through a direct Fibre Channel connection to one set of drives.
*Use VERITAS' ServerFree Agent and FlashBackup options to back up the changed blocks of the Exchange raw partition directly from the SAN to the tape library's second set of drives.
*Do the same as above for the Notes' raw partition over to the third set of drives on the tape library.
With the above configuration, you are now utilizing the fastest throughput you can. In our experience, we have seen backups happening at the rate of around one GB/min or 56 GB/hr when using LTO-1. So, it is possible to achieve these transfer rates when all components in the backup path are optimized.
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