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I have an HP DL380e Gen 8. it has 12 3.5/LFF slots on the front. The backplane has two SFF8087 cables to the HBA. I thought that SFF8087 could only carry 4 SAS channels, so how do 12 disks work over 2 SFF8087s? Does it only support 8 at a time?

Michael Hampton
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rsaxvc
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1 Answers1

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In short: the cables are to connect to the backplane, not directly to disks on that backplane. The cables don't result in a straight wire (with 1 disk on 1 lane) from HBA to a specific disk.

The HBA communicates with the backplane. The backplane has internal logic to allows the HBA address specific disks on that backplane. The protocol allows up to 255 individual disks to be addressed, so 12 is not a problem.

Analogue: the HBA is a router, the backplane is network switch, the two SFF8087 cables are redundant uplinks and each disk is connected to a unique switchport and the SAS protocol is routed over that redundant network.

https://en.wikipedia.org/wiki/Serial_Attached_SCSI#SAS_expanders

HBruijn
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