Team, FYI, I asked the same question to IBM as well
Question :- IBM TS3500 hasTS1140 IBM enterprise drive has capability to connect to 8 gbps FC ports. Could you help me to understand if we connect them on 8gbps fc port what the benefit we are getting?
& if we connect it on 4gbps port what are the pros & cons.
What is IBM recommendation on it?
Answer :-
I would say the difference difference 8Gbps vs. 4Gbps is bandwidth, and thus potential performance benefits. If 8Gbps connections are easy to implement I would recommend using them.
With 8Gbps connection you get double the bandwidth to tape drive compared to 4Gbps.
The native transfer rate of one IBM TS1140 tape drive is 250 MB/sec, so with non-compressable data a 4Gbps connection between a tape drive and server would be enough (tape drive read/write speed would be the limiting factor here).
But, if the data written to tape drive is compressible, we can then read/write actual data at much higher rate to tape. TS1140 tape drive compresses data automatically if it detects that data can be compressed
-With 1,5:1 compression ratio data is read/written to tape at 375MB/sec
-With 2:1 compression ratio data is read/written to tape at 500MB/sec
-With 3:1 compression ratio data is read/written to tape at 750 MB/sec
So when reaching compression ratios 1,5 or more you will benefit from 8Gbps connections.
A single TS1140 tape drive is capable of reaching almost 700MB/sec transfer rates.
One benefit for using 4Gbps for some customer is cable length; with 8Gbps the allowed cable length is shorter:
-With OM2 cable and 8Gbps you can put 50m cable between two Fibre Channel devices while, while with 4Gbps you can put 150m cable between two Fibre Channel devices
-With OM3 cable and 8Gbps you can put 150m cable between two Fibre Channel devices while, while with 4Gbps you can put 380m cable between two Fibre Channel devices
Question :- If cable length is not criteria, then 700mb/s is also achievable on 4 gbps port, even in practical it’s not achievable
These drives are connected in both SAN, One 4gbps cable will go to SAN1 & another 4gbps to SAN2. I hope these are load balancing mode.
Do you still see any performance issue? Do you seen practical scenario where these drives are utilized more than 700 mb or so…
Answer:
Only one tape drive port is active at one time. To reach more than 350-400MB/sec you need 8Gbps connection.
Control path failover, data path failover and load balancing are possible to use, they can be enabled by purchasing Path Failover license to TS3500 library/libraries . There are operating system restrictions on how those features can be used.
Reaching high data rates on a single tape drive depends very much on what kind of data that is being backed up and the backup application itself (compression/streaming/multiplexing/block size used with tape media etc...). Using more tape drives also typically improve performance. I have seen customers doing 500-600MB/sec on single tape drive, then again I have seen customers who can only partially utilize the high performance of TS1140 tape drives.