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I have a desktop at home with both SAS and SATA ports. (The SAS ports are supplied by a 3ware 9750 card). Currently I have 5 SATA drives connected to these. One small SSD to boot from and four larger drives to hold data.

I now want to add a SAS drive. As far as I know this should just work. However there is a lot of advice not to mix SAS and SATA on the same controllers. I understand that adding a SATA device to a previously pure SAS environment is a bad idea. But I can't find reliable information on the reverse.

Question: Is there any reason not to add a SAS drive to a SAS bus previously containing only SATA drives?

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You can mix SATA and SAS on the same controller. I do it sometimes. It works best when you have dedicated drive connections (e.g. 4-lane connectors to a non-oversubscribed backplane or to a 4-disk breakout cable).

Just avoid mixing types when a SAS expander is involved. The reasoning?

...direct attaching SATA disks to SAS HBAs should work just fine. It's when you add SAS expanders (and SATA Tunneling Protocol) to the mix that you start encountering weird errors with misbehaving SATA disks. SATA simply isn't designed with a switching fabric in mind, and it looks like firmwares still aren't robust enough to deal with command tunneling reliably in the presence of errors.

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