auto-negotiate question (hba, array, and switch)

[ponetguy2]

I have a question regarding HBAs, disk arrays, and the switch. If I have a 4G switch which can auto-negotiate, 4G HBA (I'm not sure if the HBA can auto-negotiate), and an array which peaks at 2G bandwidth, will this cause a problem? Do I need to setup the HBA to auto-negotiate to 2G, so that it can communicate with the array?

If this question is stupid, please forgive me. I'm new to SAN.

"Not all OSs suck, it's just that some OSs suck worse than others"

"Not all OSs suck, it's just that some OSs suck worse than others"

 

[ponetguy2]

forget it. i found the documentation on the hbas. both switch and hbas can auto-negotiate. even if the array is only capable of 2GB transfer rate, and the switch and hba is 4GB, the hba and switch can negotiate down to 2GB.

sorry.

"Not all OSs suck, it's just that some OSs suck worse than others"

 

[p5wizard]

AFAIK, all 4Gbit/s SAN hardware clocks down to 2Gbit/s or 1Gbit/s speed. The 10Gbit/s ports on some (e.g. McData SAN director) run a proprietary protocol and are incompatible with 4/2/1 Gbit/s ports. Those are used for high speed ISLs.


HTH,

p5wizard

 

[comtec17]

Never use Auto-Negotiate as it will use the slowest link until you saturate it. By hard coding everything to 4GB you are at least guaranteed to have that pipe for use.

Also keep in mind that just because it is 4GB, this does not mean you will push it. I have been in the SAN business for almost 10 years and there are not many shops that can push this or 2GB

 

[Breslau]

10 gig will not be compatible with anything below that, it will be a forklift upgrade when it comes around, but that is a ways off to the host, 4 gig just hit the streets this year. i suspect that most folks will go to 8 gig next and then hold on to that for a while if/when 10 is available.

you are fine to auto-neg to your host from your switch, unless you're using winderz. i have seen issues with MS boxes with auto on. you will not however get 4 gig's worth of bandwidth to your raid box until you get that guy up to the same speed. in other words you raid box and host HBA negotiate speed with their respective switch ports and not end to end. a direct line btwn the two would be a different story tho...

 

[ponetguy2]

Thank you for the advise, guys. I'll make sure I hardcode everything to 2G.

"Not all OSs suck, it's just that some OSs suck worse than others"