What is the correct SAS connector to make use of the full speed with the Samsung 1643a at my HBA?
(HPE H240 & 12G HPE expander with SFF-8087= mini SAS connector)
The official manual gives no hint - some inofficial documents say: SFF-8680 (see screenshots attached)
That makes sense, cause at least two SAS3 12G are necessary to get the full speed and SFF-8680 is certified for 2 lanes.
Yet it seems impossible to get hold of a SFF-8680 cable in Europe
I saw that the SFF-8639 should be at least physically compatible to the SFF-8680 - is it also electrically compatible, so does it carry 4 SAS lanes?
If I understand the following article correctly, it should: SFF-8639 bisher nur in Servern | heise online
Moreover I can not get hold of a SF-_8087 to SFF-8639 cable
is using an SFF-8087 cable (mini SAS 4 lanes) → SFF-8087 to SFF-8643 adapter → SFF-8643 (Mini SAS HD 4 lanes) to SFF-8639 an alternative?
What cabels are you using?
What is the most cost-effective solution?
Background: I want to connect two Samsung 1643a SAS SSD to my HPE H240 HBA to use it as L2ARC insted of an U.2 SSD I am currently using (need the PCIe lanes for something else and got the two PM1643a for a bargin on ebay)
p.s.: the naming conventions for the SFF connectors are a horrible mess
Is it not connecting ? I dont think there should be any bandwidth loss for using older connector style if it can negotiate the drive up to 12g. (Not all cables / backplanes allow this as with all cabling quality could cause issues here)
My understanding is the cabling changes are mostly density changes, the backplanes can create issues if it doesnt support 12g or multi channel, but some of the direct connect ones wont way 12g but should connect that way if its a 1-1 connection.
Thats not how SAS works, you get 1 lane per drive unless the backplane supports multi path and that gets more complicated. I don’t not fully understand multipath as I have not messed with it.
Why do you think you need 2 lanes?
Also the connector would just be w/e from your HBA → Drive direct connect (No multipath) or to some back plane that could support multi path.
So the connector your need is dependent on the HBA and your connection method.
Is the multipath part so not really a single connector, it would be built into some chassis or some weird adapter like this
I need more than one 12G SAS lane as the (max.) Data transfer Rate is 2100MB/s
Asked plainly: How to connect a single 12G SAS3 HBA to the Samsung PM1643a to get the maximum speed?
What cable shall I use?
(without any big backplane but in a homelab setting)
NB: I do not need multipath (that is for my understanding a redundancy feature with two controllers) but simply the highest speed connection to one controller (that needs at least 2 lanes in my best understanding)
But I think we need a SAS expert here.
Maybe @wendell knows how to connect to a single HBA to a Samsung PM1643a SAS drive to use its maximum speed that exceeds one lane SAS3?
SFF-8680 is effectively an older revision of SFF-8639 U.3. They both only have the pins to support to 2 SAS ports.
Theoretically you’d need a sff-8087 to dual port sff-8639 u.3 cable, but I’m pretty sure that cable doesn’t exist because the sff-8087 connector is too old and has inferior electrical characteristics compared to the sff-8639 connector.
You might find a sff-8087 to dual port sff-8480 cable that works but those seem incredibly rare.
I would strongly discourage chaining adapters together like this, while SAS is significantly more tolerant to signal degradation than SATA or PCIe, I think its pushing your luck.
All of this is assuming your HBA can negotiate a dual port connection to the SAS drive, most all newer SAS raid cards can do this directly attached to a SAS drive but I’m not 100% sure the HPE H240 can.
