Regarding the tape drives and compression -- this is the part that confuses me.
I can max-out an LTO-3 drive at native write speed at 80MB/s with no problem using pre-compressed data (compressed Sybase dbdumps), even with a measly 64kb block size. This is using direct NDMP with 2 Gb/s fc IBM LTO-3 drives. Using contrived data, i.e. large files dd'ed from /dev/zero or hpcreatedata, I have in the past maxed out 2 Gb/s LTO-3 drives at approximately 170 MB/s, as you claim above. However, this was using 256kb block sizes. I have read reports where 2 Gb/s LTO-3 drives can be pushed to 220-230 MB/s using the maximum block size supported by LTO-3 (2 MB) and contrived data. Now, if compression is done at the drive, I would think that with a 2 Gb/s interface, it should be able to receive data at roughly 170 MB/s, but since the drive natively spins at 80 MB/s, it would compress that data, 4x, as you claim, to get that 240 MB/s top end. But, in my mind, using 2 Gb/s or 4 Gb/s shouldn't make a bit of difference for a drive that natively writes at 80 MB/s. Does anyone else have experience with this? Also, I've seen LTO-3 tapes in our environment marked as "FULL" by Netbackup with close to 2 TB of data on them. -- nick Yep, I'm using jumbo frames. The performance was around 50% lower without it. I'm not currently using any switches for 10GbE, the servers are connected directly together. Re 4Gb vs 2Gb tape drives - since the data is compressed at the drive, we still need to be able to transfer the data to the drives as fast as possible. The highest throughput we've been able to get with a single 2Gb fibre HBA is about 190MB/s (using multiple 2Gb disk-subsystem ports zoned to a single HBA port). The highest throughput we've gotten with a single 2Gb tape drive is 170MB/s. Since this is near the peak we can get with 2Gb, I assume that the 2Gb interface on the tape drive is what's limiting our throughput. Also, we get about 4x compression of this data on the tapes (~1600MB on an LTO3 tape). So, with 265MB/s at 4x compression, the physical write speed of the drive is probably somewhere around 65MB/s (265/4). Since the tape compression ratio has remained the same with both 2Gb and 4Gb drives, I'd guess that the physical drive speeds with the 2Gb drives were probably closer to 40MB/s (170/4)... -devon _______________________________________________ Veritas-bu maillist - Veritas-bu@mailman.eng.auburn.edu http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu