Cables and ports needed for SAS drives

[supraman95]

I am trying to see what all I need to hook up new SAS Ultrium 3 920 drives. I currently have a DL360 with a P800 SAS controller with two ports. My storage works container will hold 4 of the Ultrium 3 920 SAS drives but it acts as if you need a seperate cable for each one to connect to the server. Therefore if I have all 4 drives in teh storage works will I need to P800 controllers in order to get them all connected?

[Curtis Ballard]

For tape automation we have the AN975A 2-meter cable that will connect 1 P800 ports to 4 different tape drives or the AN976A 4-meter version of the same cable.

I'm not familiar with the standalone drive enclosures but I thought the rack mount chassis had a built in expander so that you could use the standard x4 cable to that and then it was split internally to the drives.

If you really have 3 drives with mini-SAS external connectors that you need to connect to the P800 the cable mentioned above isn't listed with standalone drives but is qualified for use with the exact same drives in automation and will work fine.

[supraman95]

Thanks for the info. I spoke with an HP rep today and I was told that they strongly recommend you run one SAS tape drive per SAS port. How much speed do you lose or are their any ill affects with using the Single to 4 port cables?

[Curtis Ballard]

I haven't seen any performance degradation for running 4 tape drives on a single P800 port. SAS puts 4 full speed links on a single external connector. Internally those would be split into 4 different cables and the cable I mentioned does exactly the same thing externally. Since the data does all go through the same PCIe channels some HBA's could experience a little degradation will all channels running full speed if they can't actually use the full PCIe bandwidth, but I haven't seen that with the P800 and I have run a P800 with the cable I pointed you to in the earlier message talking to 4 HP SAS tape drives.

Most arrays use all 4 links and share the bandwidth but tape drives only need or use 1 link so when you connect 1 tape drive the other 3 links are sitting idle.

I don't understand exactly what your configuration is. I know we don't recommend the split cable for standalone tape drives but that's only because there wasn't a known configuration that required it. I'll check with the people that set the supported configurations and see if we overlooked something.