External SSD JBOD Rack

[CookiesLikeWhoa]

Hello All!

I currently have a Supermicro 216E16-R1200LPB that I'd like to use for an SSD shelf in my rack for another Freenas I'm working on. I know I read somewhere that external shelves and SSD's don't go well together due to the length of the connections causing latency issues, but I can't find that link anywhere any more, or the lengths that issues start at.

Currently the chassis is sitting right below where the freenas is located in the rack. The external connection is no more than .5M. Am I asking for trouble here?

 

[HoneyBadger]

Latency from cable length is negligible even at the "SAS max length" of 10m. Half a meter is nothing to worry about.

I'd be far more concerned about a bandwidth bottleneck at your expander. With 24 bays you can saturate a 4-lane uplink without even really trying.

 

[CookiesLikeWhoa]

Hmm I swear I read that SSD's ran into latency issues on external shelves. Either way that's excellent news!

Well right now I'm not too worried about that bottleneck. 24Gb/s should hold us over for a decent amount of time and while we have a 10Gb/s network here, realistically there should only be a few times a day all 4 editors are slamming the network at once. Mainly I'm planning on using it for ISCSI targets for a Windows Server.

 

[HoneyBadger]

I'd wager that most cases of high latency on external shelves are either due to bandwidth congestion (multiple trays of SSD behind cascading expanders) or bad parts (loose, bent, or broken cables) - just a single tray of SSD as the first external shelf shouldn't really add anything. I imagine network latency (even on 10Gbps) will mask any SAS latency.

 

[CookiesLikeWhoa]

Awesome! Thank you for all the help.