What does Hot Swap for SATA in UEFI actually do?

Operating Systems & Open Source
1

In most UEFI firmware there is an option to enable hot swap for SATA drives. If you enable it then Windows gives you the option to dismount the drive, but you can just make it offline with the same effect. Similarly in Linux, hot swap enabled or not, you can dismount the drive and unplug it.

SATA drives must support hot swap as per the spec. Never found one that doesn’t. However, operating systems don’t seem to notice when drives are plugged in to a SATA port with hot swap disabled.

So is that the sum total of what it does? It’s just a flag that indicates to the OS that it should support hot swap on that port, or enables detection of drives being plugged in inside the SATA controller, something like that?

I suppose a better way of asking it might be “are there any disadvantages to enabling hot swap?”

2

The answer to that is no. Which leads to a counter question: “Why wouldn’t you have SATA hot swap enabled by default?”

3

Or even, “why does the option to disable hot swap even exist?” if there is no down side.

The only thing I can see is that if you enable it, Windows lets you “eject” the drive, and it’s possible to accidentally select the wrong drive when trying to unplug a USB one.

4

Windows may also automatically disable write caching for “removable” drives.

2 Likes
5

That’s an interesting point. It seems to depend on a combination of factors, of which the drive being removable is one.

6

I would guess that enabling hot swap would also enable the “safely remove” option in the task bar.

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It’s surprising to me there is a way for the OS to poll whether a port is “hotpluggable”! I guess it’s at the very least a feature meant for “external SATA” aka eSATA. I think it’s kind of a shame this standard didn’t catch on. My 2011 mobo had one port at the front of the case.

If you say hotpluggable or not still works the same – dunno. It could have otherwise allowed firmware to electrically turn off the port (polling) for power savings. It’s kinda crazy if you compare idle desktop vs laptop power consumption.