Dual Port SAS SSDs

redeamon

Active Member
Jun 10, 2018
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Hey Folks,

I'm getting a bunch of Dual Port 12gb/s SAS SSDs with read performance of 1.9GB+/sec. How does one get this level of performance from SAS3 via dual port? Are there any controllers out there that support "performance" dual port? I know on some platforms dual port is used for redundancy but are there any that utilize dual port for performance?
 
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Spartacus

Active Member
May 27, 2019
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So if I'm interpreting your question correct, depending on the cable/controller most support 4 lanes, so SAS 3.0 is 4x 12Gbit/s which is about 4.8GB/s total throughput or in the case of dual port 2x 12Gbit/s or 2.4GB/s which exceeds your 1.9GB/s ask.
There aren't many SSD I'm aware of pushing the 4.8GB/s limit even on the U.2 level, hence why most backplanes/expanders use it for redundancy rather than performance, its not really needed.
 

redeamon

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Jun 10, 2018
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I might be wrong, but I don't think SAS3 pushes 4 lanes to each device. It seems that each device gets 1 lane- so roughly 1500mb/sec (theoretically). In real life I've never seen over 1gb/sec on any SAS3 SSD. Maybe I'm doing something stupid or my systems need tuning? All my Dell r630's have expanders so that plays a factor, but I've done direct connections via a LSI 3008 and it's still capped around 950mb/sec.

Any ideas?
 

Spartacus

Active Member
May 27, 2019
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Austin, TX
You’re correct, was just saying each cable can do that throughput technically, so a true dual lane device/cable should be able to do 2400Mbit/s (likely closer to 2k realworld).

Not sure on the R630 limit or specifics.
 

azev

Active Member
Jan 18, 2013
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to use both sas port on dual port ssd you have 2 options;

1. Use dual port backplane
2. Use SAS cable with dual port such as this

After you figured out the physical topology you need to make sure you have a software that supports SAS MPIO like Windows servers or any linux variance.