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The ASUS RS720-E12-RS24U server comes with 24 2.5‘‘ drive bays. The specification on the ASUS web page says that only 8 of the 24 bays support SAS drives. However, according to the manual, (chapter 2.9, page 2-55), there are 6 mini SAS HD connectors on the backplane, which together would provide enough SAS channels for all 24 bays. The E11 model comes with a similar limitation, but also with enugh SAS connectors on the backpane.

Where does the limitation to 8 SAS drives come from? Could the backplane actually support up to 24 SAS drives through the mini SAS HD connectors, provided there are enough ports on additional HBAs or RAID controller cards? That would be really useful when you have already SAS storage available to reuse in the server.

Sefe
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2 Answers2

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That server is NVMe-optimized, so the purpose of buying it would be to use up to 24 NVMe drives.

Note the references to "Tri-mode" controllers.

What are you trying to do with this system?

ewwhite
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  • I would use it in a cluster, with some nodes equipped NVMe. But others would use SAS SSDs from legacy servers. Preferrably I would use the same type of servers for operational reasons. – Sefe Jun 24 '23 at 19:44
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Where does the limitation to 8 SAS drives come from?

To my knowledge the U.2 format of the NVM SSD that is not compatible with SAS. It is either/or.

There is a U.3 format coming, that supports all 3 types, but that again is IIRC not compatible with U.2 ;)

So, it is actually a physical limitation. Happens when they did the SAS drives they did not foresee the needed space for NVM connections.

TomTom
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  • The backplane actually does support SAS, SATA and NVMe at least on some of the drive slots. It depends on that actual backplane cabling. So while NVMe and SAS are not interchangeable, you can configure the backplane to support either. My question is about whether there are more options than documented in the manual. – Sefe Jun 24 '23 at 21:56
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    "My question is about whether there are more options than documented in the manual." - no, that is not your question. Your question is up there in the question. If you want to know about options NOT given in the manual - ASK THE MANUFACTURER. – TomTom Jun 24 '23 at 22:03
  • "The backplane actually does support SAS, SATA and NVMe at least on some of the drive slots." - that makes NO Sense. It obviously does so - it is split in 3 areas of 8 wit different configurations, AS DETERMINED BY THE MANUFACTURER. "It depends on that actual backplane cabling." - no, it depends on the electronic INTERFACES to the hard discs. That is the other side compared to the cabling. – TomTom Jun 24 '23 at 22:04