SAS to SATA cables: Forward or Reverse Which, Where, Why

[barrygordon]

There have been many posts involving SAS to SATA breakout cables of the Forward vs Reverse types.  Which type to use where is generally the question.

 

To make it simple, if the host-controller side is a SAS connector (SFF-8470) and the target side is SATA drives then you must always use a SAS to SATA Forward Breakout Cable.  If The Motherboard/host-Controller side are SATA connectors and the backplane is a SAS connector then you must always use a SAS to SATA Reverse Breakout Cable.  For SATA to SATA you just use a "SATA" cable as there is only one type, although they do come in different lengths. For SAS to SAS connections there is also just a single cable type.

 

The two breakout cables, forward and reverse,  are not the same although they look outwardly to be the same, not withstanding the fact that some of these cables have the SATA portion of the cables at staggered lengths and some have them at fixed length.

 

If you just want to follow the rule you can stop reading now.

 

Why are there two different cable types for SAS to SATA connectivity?  An objective of the SATA system design was that SATA cables would have identical connectors at each end, and that SATA devices would have identical connectors independent of whether they were disk drives or disk controllers.  This helps to make interconections foolproof and reduces the cost of cables.

 

If you ever look at a SATA to SATA cable they are identical and wired as a 1:1 cable. In a 1:1 cable pin 1 of end-A goes to pin 1 of end-B, pin 2 to pin 2, pin 3 to pin 3, etc.  If you were to look at the SATA connector on a host-controller or motherboard and the SATA connector on a disk drive they look the same, and are physically the same, but each are wired differently.

 

A SATA connector has 7 pins. Two of the pins make up the receive pair and two of the pins make up the transmit pair.  The other three pins are all used for ground signals. If a 1:1 ("straight-through") SATA to SATA cable is to work, then the receive pair can not be the same pins on each of the two device connectors (Host vs disk)! If they were the same pins then we would need what is generally referred to as a "cross-over" cable.  The "Absolute Rule" is that the transmit pins on one side must connect to the receive pins on the other side and vice versa. This is true for PC-PC RS232 connections, Ethernet Connections, SATA connections, and almost all types of serial connections which are duplex, i.e. separate receive and transmit cables. 

 

The SATA cable connector design puts the Host/controller side transmit pair on pins 2 & 3, and the Receive pair on pins 5 & 6.  On the Disk drive the receive pair are pins 2 & 3, and the transmit pair are pins 5 & 6. As a point of reference pin 7 is the keyed pin.

 

All SAS connectors have their pins structured the same way no matter if they are on a host controller card, or a SAS backplane. Since for each port of the four that make up the SFF-8470 connector the transmit pins and the receive pins are physically in the same location, and we must connect SAS transmit to SATA receive and SAS receive to SATA transmit (for each port); the cables must be different depending on whether the SATA connector is on a disk drive or a Motherboard/Host-Controller.

 

A SAS to SAS cable must therefore be a "cross over" cable to connect the transmit pairs of a port to the receive pairs of the corresponding port on the other side.

 

Hope that helps clear up the mystery.

[Lantesh]

Great info.  Thanks for posting it.

[kolepard]

Very helpful.  Thank you.

[JanBanJuveh]

Hello. I have just bought a LSI SAS3081E-R raid controller. And have also bought an SFF-8087 to SFF-8482 cable. Is there also forward and reverse cables for this one? Because my drives are not being detected by the raid controller card.

[uldise]

6 hours ago, JanBanJuveh said:

I have just bought a LSI SAS3081E-R raid controller.

looks like it's an old controller and wont support larger drives than 2TB... and you need to flash it to IT mode, if such ever exists.. quick google says it exists..

see here for example: https://lime-technology.com/forums/topic/3016-update-works-with-errors-lsi-sas3081e-r/

 

[CSIG1001]

might have to hold out on cables until i verify the backplane on these norcos 4224 

 

they might come with mini sas now

 

worse comes to worse i will keep a few cables and send back the rest for future use.

 

 

Edited June 30, 2018 by CSIG1001

[SSD]

On 7/14/2010 at 11:59 PM, barrygordon said:

There have been many posts involving SAS to SATA breakout cables of the Forward vs Reverse types.  Which type to use where is generally the question.

 

To make it simple, if the host-controller side is a SAS connector (SFF-8470) and the target side is SATA drives then you must always use a SAS to SATA Forward Breakout Cable.  If The Motherboard/host-Controller side are SATA connectors and the backplane is a SAS connector then you must always use a SAS to SATA Reverse Breakout Cable.  For SATA to SATA you just use a "SATA" cable as there is only one type, although they do come in different lengths. For SAS to SAS connections there is also just a single cable type.

 

 

The controller card of most of the HBAs recommended on the forums  have SFF-8087 connectors - not SFF-8470.

 

And I'll mention those forward breakout cables (SFF-8087 to SATA) are often available at MonoPrice much cheaper than elsewhere.

[websurfer83]

Hello @all,

 

I am new to this site. I found it with a Google search "sff-8087 reverse forward". Now I need your help because in another community in German language nobody could help me.

 

Some time ago I bought this external drive case:

https://shop.yakkaroo.de/External-SAS-drive-chassis-with-three-drive-bays-SFF-8088

On the inside it has a SFF-8087 connector and on the outside SFF-8088.

 

In my computer there is a SATA controller which I want to use. So I ordered this item:

https://shop.yakkaroo.de/mini-sas-slot-bracket-adapter-SFF8088-to-SFF8087-full-height

 

For the connection between the computer and the external case I would like to use this cable:

https://shop.yakkaroo.de/mini-sas-connector-cable-external-sff-8088-1m

 

But now there are missing two cables:

1. For the connection in my PC I need a cable 4 x SATA -> SFF-8087.

2. And in the external case I need a cable SFF-8087 -> 4 x SATA.

 

But I am not sure which cable is the right for me. This very short posting says:

FORWARD ==> single connector on controller and then fanout to multiple drives with SATA connections.

REVERSE ==> multiple SATA ports on controller combined into one connector for the backplane.

 

Am I right that I need both types?

 

1. For the connection in my PC I need a cable 4 x SATA -> SFF-8087.

==> Here I think I would need a REVERSE cable. Would this be the right choice?

2. And in the external case I need a cable SFF-8087 -> 4 x SATA.

==> Here I think I would need a FORWARD cable. Would this be the right choice?

 

Or am I wrong?

 

I hope you could please help me.

 

Thanks and kind regards

websurfer83.

 

[JorgeB]

7 minutes ago, websurfer83 said:

Am I right that I need both types?

Yes, you need one of each.

[JorgeB]

8 minutes ago, websurfer83 said:

Am I right that I need both types?

Also note that max length from controller to disks for SATA devices is 1 meter.

[websurfer83]

@JorgeB:

Thank you! I want to use three drives in the external case:

DVD-ROM, MO, ZIP. For some of them I need an IDE-SATA-converter. They use only SATA 1,5 Gbit/s. I hope that it will also work with 2 meters of cabling. eSATA also works with 2 meters or even more, SFF-8088 is even better cabling than eSATA.

[ich777]

9 minutes ago, websurfer83 said:

@JorgeB:

Thank you! I want to use three drives in the external case:

DVD-ROM, MO, ZIP. For some of them I need an IDE-SATA-converter. They use only SATA 1,5 Gbit/s. I hope that it will also work with 2 meters of cabling. eSATA also works with 2 meters or even more, SFF-8088 is even better cabling than eSATA.

Note that we also got a German section.

Sei dir bewusst das SATA anderen spezifikationen unterliegt als SAS bzw. Auch eSATA

[websurfer83]

@ich777:

Thank you. I did not knew that there is a German section. I posted in this topic because Google found it for me

 

Ja, ich weiß, SATA hat andere Spezifikationen als SAS, aber selbst eSATA über eine normale Slotblende ohne dedizierte eSATA-Ports auf dem Controller läuft mit einer Kabellänge von 2,5 Meter in der Regel problemlos (0,5 Meter intern vom Controller zur Slotblende und nochmal 2 Meter extern zum Gerät).

[CanadianMoose]

Years later, this post answered a question I didn't know I had before I ended up buying the wrong thing and not understanding why it didn't work.  Thank you @barrygordon for explaining the details so I didn't have to go through a major headache!

[Paul Reid]

The question that never seems to get answered anywhere is if you have a SAS RAID controller using a miniSAS connector going to a 12Gbps SAS backplane that uses SATA connectors and the typical MiniSAS to 4 x SATA cable, then populate the drive bays with 12Gbps SAS drives, will the controller see 12Gbps SAS, or will it see 6Gbps SATA? I'd imagine it'd see 12Gbps SAS - otherwise why would a manufacturer make a 12Gbps SAS backplane with SATA connectors at all? Anyone have any insight into how this works out?

[JorgeB]

10 hours ago, Paul Reid said:

then populate the drive bays with 12Gbps SAS drives

If the backplane is SATA only it won't accept SAS drives, they won't fit, but most backplane are SAS, and they also accept SATA.

[doron]

11 hours ago, Paul Reid said:

...populate the drive bays with 12Gbps SAS drives, will the controller see 12Gbps SAS, or will it see 6Gbps SATA?

Either the BP will not physically accept SAS drives to begin with (as noted by @JorgeB above) due to the connectors being SATA only, or the controller will see a SAS drive(*).

Neither the cables nor the BP will change the protocol spoken by the drive from SAS (essentially, SCSI) to SATA (essentially, ATA).

 

(*) In some cases, speed might be negotiated down (e.g. 6Gb/s SAS instead of 12Gb/s SAS).

[ChrisP21]

Hi Folks,

 

Is there a reverse breakout equivalent for the SFF8643 connector?  I am trying to connect the LSI2308 SAS2 controller (8 L-SAS ports for an interface) to the Intel RES3FV288 SAS Expander which takes SFF8643 for input and output. 

 

I have these SFF8643 to 4x SATA cables but the drives are not being detected.  I am struggling to find a "reverse breakout" equivalent for SATA/SAS to SFF8643(mini SAS HD).

 

My motherboard is an X10SL7-F with an onboard LSI 2308.  The RES3FV288 is plugged into one of the PCI slots for power only.  The card has already been flashed to IT mode.  One person on suggested I may have plugged the SATA ends of the cable I have into the wrong numbered ports on the LSI2308 controller so I will try that next.  They said the card cards input cable F to be plugged into SAS ports 0-3 and I had it plugged into SAS ports 0,2,4 and 6.  I will change it up to see if it makes a difference.

[JorgeB]

15 hours ago, ChrisP21 said:

s there a reverse breakout equivalent for the SFF8643 connector?

For example:

https://store.supermicro.com/supermicro-internal-reverse-breakout-cross-over-minisas-hd-to-4-sata-with-sideband-55-55-55-55-55cm-cable-cbl-sast-0631.html

[dopeytree]

What happens if I add a reverse sas cable in this configuration: LSI card or expander --> motherboard's sata ports.

Does this do anything? The LSI card is connected via the PCIe lanes but limited in bandwidth.. is anything gained or would it not do anything?

 

So like photo but then also adding in the reverse sas cable to motherboard's sata.

Edited June 21, 2023 by dopeytree

[JorgeB]

11 hours ago, dopeytree said:

Does this do anything?

No.