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On a Win7 laptop, when I plug in any external USB3 platter-based hard drive into a...

  • USB3 port, and then click on the Eject option in the system tray (and receive the Windows message that it safe to remove), the activity light on the drive will go into a slow-flash mode, indicating that all data has been written, the heads are parked, and it is safe to unplug. I can also hear and feel the platters stop spinning.

  • USB2 port, and then click on the Eject option in the system tray (and receive the Windows message that it safe to remove), the activity light on the drive will remain steadily on and I can hear and feel the platters continuing to spin.

How can I get drive removal to function the same on the USB2 ports as the USB3 ports?

After Windows says the drive is safe to remove, is there any harm in unplugging the drives when connected via USB2, even though the drive indicator light remains on?

  • I think Windows has an option to allow Quick Removal (safe to unplug even without ejecting, default option), or use Better Performance (needs to eject to remove safely) for your USB drive. – ionizer May 7 '18 at 19:37
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    "the activity light on the drive will go into a slow-flash mode, indicating that all data has been written, the heads are parked, and it is safe to unplug." ... oh yes? you're sure that's what it means? – Attie May 7 '18 at 20:24
  • @Ramhound Both. I tried it with the same exact device being connected as well as two different devices of the same model. The results were the same. – RockPaperLizard May 7 '18 at 21:28
  • @Attie Pretty sure. I can hear and feel the platters stop spinning after ejecting from the USB3 port, but definitely still spinning after ejecting from the USB2 ports. – RockPaperLizard May 7 '18 at 21:35
  • @Ramhound I added some text in bold italics above as well. – RockPaperLizard May 7 '18 at 21:36
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An USB enclosure with SATA hard drive isn't a simple system. It contains a complex "bridge" between USB interface and SATA interface. For this mass storage device to be ready for USB transactions, the bridge usually contains a serious MCU, which does basic SATA configuration by itself and builds proper data tables about attached disk capabilities/formats etc. in a suitable USB Mass Storage Class format. This includes power management.

Below is an example of USB3-SATA bridge produced by Fujitsu:

enter image description here

This bridge operates under control of 32-bit ARM™ Cortex-M3™ processor.

As one can see, the bridge supports both USB 3.0 and USB 2.0 interfaces, which are running through the same USB 3.0 connector. Therefore there are some differences how the bridge can handle attach/de-attach-shutdown sequencing.

The issue is that due to essentially half-duplex interface of USB 2.0 and lack of deferred out-of-order completion of bus transactions, USB 2.0 link can implement only the legacy Mass Storage Class Bulk-Only Transport (BOT) specifications. The USB 3.0 bus protocol has enabled the USB Attached SCSI (UAS) specifications, which allow much wider functionality of SATA drives.

I am pretty sure your system loads a UAS driver over USB 3.0 link, and resorts to BOT functionality if the enclosure is attached over USB 2.0 link. Different drivers (or driver modes) produce slightly different behavior after the "eject" operation.

However, I am pretty sure the firmware in the USB-SATA bridge chips makes certain that after receiving the "eject" command everything is flushed and parked accordingly, otherwise the enclosure developers would go out of business pretty quickly. Therefore if a system says "it is safe", then do disconnect the drive with confidence.

  • Great answer. Thanks. To clarify, even if the drive platters are still spinning, as long as the system says "safe to remove", then it's okay to pull the USB cable (which removes the power as well)? – RockPaperLizard May 8 '18 at 6:37
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This comes down to two things that may happen behind the scenes:

  1. The filesystem cache has been written to disk, and the filesystem has been cleanly unmounted.
  2. The USB device has been disconnected by the host, and the device is now in the "detached" state (i.e: not enumerated).

From your description, I would suggest that:

  • Your USB 2.0 port(s) are completing step 1
  • Your USB 3.x port(s) are completing step 1 and step 2

This could be due to a number of things, and it's difficult / impossible to determine precisely what... i.e: If the USB to SATA bridge is a USB 3.x-compliant device, then it's set of operational states will be different when connected to USB 2.0 vs. USB 3.x. Chances are that you cannot get it to behave the same for both.

As far as the filesystem's integrity is concerned, it is fine to unplug after step 1.

However, even after step 2 it's impossible to be 100% sure that the disk itself (not the USB to SATA bridge, or whatever is employed) is truly idle - heads parked, and platter not spinning.

  • Thanks. So it's fine to pull the drive's cable even with the platters spinning (as long as the the filesystem's cache has been written)? – RockPaperLizard May 7 '18 at 21:40
  • @RockPaperLizard, if platters are spinning, it doesn't necessarily mean that the drive is doing any data manipulations. – Ale..chenski May 8 '18 at 0:23
  • The heads can be parked while the platters are still spinning. The best you can reasonably do is wait for the notification and then unplug... possibly wait 1-2 seconds after, but there shouldn't be any need... – Attie May 8 '18 at 8:10
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After Windows says the drive is safe to remove, is there any harm in unplugging the drives when connected via USB2, even though the drive indicator light remains on?

If you have safely ejected the device and received the notification indicating it is safe to remove the device, then it is safe to disconnect the device.

How can I get drive removal to function the same on the USB2 ports as the USB3 ports?

USB 2.0 and USB 3.0 devices are not identical. Which means the way they are disconnected from the host are not identical. What you want is not possible.

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