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storage - How exactly does a SAS SFF-8087 breakout cable work? + RAID/connection questions



Please let me know if my question does not makes any sense as I am not sure if I am interpreting it correctly from my thoughts due to my lack of technical knowledge on this.



If I am using a motherboard which has a connection for a SFF-8087 to 4x cable such as this SFF-8087 to 4x SATA connection.



I am still learning about SAS but was told to build a system from a potential employer utilizing these connections. However, I am just not sure I understand the concept on how the system will treat the SATA connections which are going into the SAS port via this cable.




Also what would be the advantage of doing it this way as opposed to just connecting the SATA drives directly into the SATA motherboard ports? I believe the built-in SAS connection may be an integrated RAID controller.



Although, yes I can just go ahead and connect all the cables that fit I would like to have a better grasp of what I am doing such as:




  1. If a motherboard has SAS connections, should I automatically assume it has some type of RAID controller built-in or is this on a case by case basis?

  2. Do All RAID controllers have only SAS connections?

  3. Even though the SATA drives are connected via a SAS connection, are they still just treated as SATA drives or as SAS technology?



Answer



A few items to help clarify SAS technology...




  • SATA drives can connect to SAS ports.

  • SAS drives cannot connect to SATA ports.

  • Server-class hardware typically uses an embedded RAID controller or a separate RAID controller PCIe device.

  • Most RAID controllers and SAS HBAs will use SAS connections (multilane or 4-lane SAS ports).

  • Internally, these systems will use one of the internal SAS transports (SFF-8087 or SFF-8484) for cabling.

  • 4-lane SAS cables carry FOUR SAS links over the same cable.


  • Enterprise servers will typically have a SAS backplane for hot-swap hard drives. These backplanes can accommodate SAS and SATA disks. The backplanes also provide power to the drives. It doesn't make sense to run SATA cables to hot-swappable hard drives. Instead, the internal SAS cables will link the controller and the backplane.

  • You can mix and match SATA and SAS on the same backplane, but because the protocols are different, bad things. can happen.



Internal SAS 4-lane cabling to a backplane
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Internal SAS breakout cabling to a backplane

enter image description here


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