I've got a Dell SAS 6/iR PCI-E adapter. I don't have a multiplier backplane. I'm planning on connecting SATA (non SAS) drives. If I buy cable adapters only (ones that split a SAS connector on the card to a certain number of SATA cables), how many drives can I connect to this card?

The way I see it, there are two limitations: a limitation imposed by the theoretical max number of devices supported on the card (which I've dug through the specs to find, but haven't seen yet), and a limitation imposed by the number of SAS plugs on the card multiplied by the number of SATA cables that come out of the highest-multiplying splitter I can buy. The answer to my question would be the minimum of those two limitations.

I've seen 4x SATA coming out of some splitters; are there any that have more?

Alternatively, if this is an RTFM question, does anyone have a good link to a "this is how SAS works, this is how you figure out the max number of devices, and this is how the concepts of 'ports', 'lanes', 'endpoint devices', and 'connectors' all relate in SAS-land" document? I've looked around on the Dell docs, but haven't found anything that explains this to someone at my level of understanding of SAN/enterprise storage technologies.



Depending on the connector in use the maximum number of SATA drives that can be connected (without active electronics) to a SAS port is 4. If you use an external SAS expander and cascade connections then you can support a very large number of drives (255 SAS / 1020 SATA). Add in a SAS switch and the number goes much higher.

This is really an academic question, though, as the practical number of drives supported on a channel will be limited to a much smaller number as individual servers will tend to scale horizontally with additional SAS ports or up a more traditional SAN or enterprise NAS with a dedicated storage array.

The Wikipedia page on SAS is actually pretty good - http://en.wikipedia.org/wiki/Serial_attached_SCSI . I'd suggest starting there.

  • By "SAS port", do you mean physical connector, or port as in "4 port internal SAS connector"? – Zac B Jun 3 '12 at 1:04
  • There are several physical connectors that can be used for SAS connectivity (as seen in the provided link). Adapters can be had for most of them to split out to four SATA connectors. – rnxrx Jun 3 '12 at 1:10

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