Any Problem Using Two External USB-Powered HDDs on rMBP?

Started Mar 29, 2013 | Discussions
RustierOne
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Any Problem Using Two External USB-Powered HDDs on rMBP?
Mar 29, 2013

On my rMBP (2.3 GHz, 250 GB SSD, 16 GB memory) I've have been using an OWC Mercury On-the-Go-Pro enclosure with Seagate Momentus 750 GB 7200 rpm USB 3.0 HDD for Time Machine backups. It's partitioned 100 GB general storage and 650 GB TM backup. Since I also have a Toshiba 750 GB 5400? rpm USB 2.0 HDD, I've began using it partitioned the same for alternate TM backups. Both are bus powered and are seeming to work just fine, despite OWC's warning against bus powering more than one HDD at a time.

Question: Is there any problem running these HDDs at the same time, both bus-powered?

I really like having both powered up on the 2 USB ports, alternating TM backups every hour. But being somewhat cautious, I'm wondering if I could be damaging anything with this setup. So far the only problem is remembering to eject all 4 partitions before shutdown.

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Best Regards,
Russ

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BeachnCruz
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Re: Good luck ... I prefer to opt for AC Power Adapters
In reply to RustierOne, Mar 29, 2013

RustierOne wrote:

On my rMBP (2.3 GHz, 250 GB SSD, 16 GB memory) I've have been using an OWC Mercury On-the-Go-Pro enclosure with Seagate Momentus 750 GB 7200 rpm USB 3.0 HDD for Time Machine backups. It's partitioned 100 GB general storage and 650 GB TM backup. Since I also have a Toshiba 750 GB 5400? rpm USB 2.0 HDD, I've began using it partitioned the same for alternate TM backups. Both are bus powered and are seeming to work just fine, despite OWC's warning against bus powering more than one HDD at a time.

Question: Is there any problem running these HDDs at the same time, both bus-powered?

I really like having both powered up on the 2 USB ports, alternating TM backups every hour. But being somewhat cautious, I'm wondering if I could be damaging anything with this setup. So far the only problem is remembering to eject all 4 partitions before shutdown.

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Best Regards,
Russ

OWC advice is generally good. AC Adapters are an inexpensive way to improve your odds for avoiding a possible future HD/Time Machine/backup issue. I only occasionally depend on ext HD bus power if on the road and away from a reliable AC power source.

OWC AC Power Adapter

Jim

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Najinsky
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Shouldn't be a problem
In reply to RustierOne, Mar 29, 2013

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

I often run 2 USB drives, both previously with the MBA and now with a rMBP. Never any issues.

You can use System profiler to see how much current the external drives require and how much is available to them. Make sure both drives are plugged in then:

Apple Menu->About this Mac->More-Info->System Report...

Then click on USB in the left column under hardware, and then on each connected drive in the right column to see what it requires and what's available.

My WD 2TB external drive requires 224mA with 900mA available (standard for USB3 on the rMBP). On the USB2 MBA it was 500mA available (USB2 standard, but for the superdrive, it also shows 600mA as  'Extra Operating Current').

-Najinsky

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mihama01
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Re: Shouldn't be a problem
In reply to Najinsky, Mar 31, 2013

Didn't know about the system report trick, useful info, thanks

Another alternative is to use a powered usb hub, which will provide power to the devices and also charge you iPhone and other devices, saves on power bricks, wiring  etc.

Cheers

S

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Doug R
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Re: Shouldn't be a problem
In reply to Najinsky, Mar 31, 2013

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

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Doug

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Najinsky
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Re: Shouldn't be a problem
In reply to Doug R, Apr 2, 2013

Doug R wrote:

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

So you're saying this (http://en.wikipedia.org/wiki/Universal_Serial_Bus) is wrong?:

"A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. A low-power device draws at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. A high-power device draws, at most, the maximum number of unit loads the standard permits. Every device functions initially as low-power—but may request high-power, and gets it if it's available on the providing bus.

Some devices, such as high-speed external disk drives, require more than 500 mA of current and therefore may have power issues if powered from just one USB 2.0 port: erratic function, failure to function, or overloading/damaging the port. Such devices may come with an external power source or a Y-shaped cable that has two USB connectors (one for power+data, the other for power only) to plug into a computer. With such a cable, a device can draw power from two USB ports simultaneously."

And you're saying this (http://support.apple.com/kb/ht4049) is wrong?:

"

Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

  • Apple MacBook Air SuperDrive (when connected to supported computers)
  • Aluminum Wired Keyboard*
  • iPod
  • iPhone
  • iPad

To meet requests for additional power from these Apple peripherals and devices, some Apple computers and displays can provide up to 1100 mA at 5 V through the port to which the Apple peripheral or device is connected. This power is available under certain conditions:

  1. An Apple peripheral device must be plugged directly into an Apple computer or display. Apple peripheral devices connected to hubs will not have access to extra power above the standard USB specification of the port the device is connecting to (500 mA for USB 1.1 or 2, 900 mA for USB 3).
  2. Your Apple computer or display must be powered on and must be awake. If your Apple computer or display is asleep, all ports will provide their normal maximum output. If your Apple computer or display is powered off, no power will be provided.
  3. The port providing extra power is determined by the first Apple peripheral or device to connect to the Apple computer or display that requires power beyond 500 mA for USB 1.1 or 2, or 900 mA for USB 3. The remaining ports will continue to offer their normal maximum output. Some Apple computer and displays may offer the ability to operate more than one USB port at 1100 mA at 5 V. On those computers, the second or third port is enabled when an appropriate device is connected."

-Najinsky

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gaussian blur
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Re: Shouldn't be a problem
In reply to Najinsky, Apr 2, 2013

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

And you're saying this (http://support.apple.com/kb/ht4049) is wrong?:

Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

  • Apple MacBook Air SuperDrive (when connected to supported computers)

That part is wrong. The external SuperDrive only works on supported computers, which are Macs that lack an internal DVD drive, unless you patch a plist or replace a custom bridge chip. It has nothing to do with power requirements.

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Najinsky
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Re: Shouldn't be a problem
In reply to gaussian blur, Apr 2, 2013

gaussian blur wrote:

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

And you're saying this (http://support.apple.com/kb/ht4049) is wrong?:

Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

  • Apple MacBook Air SuperDrive (when connected to supported computers)

That part is wrong. The external SuperDrive only works on supported computers, which are Macs that lack an internal DVD drive, unless you patch a plist or replace a custom bridge chip. It has nothing to do with power requirements.

No it's still right, it draws 600mA (shown as Extra Operating Current), 100mA above specification. The reason the hack works is because even Macs with an internal superdrive now provide extra operating current for charging iPhone and iPads.

-Najinsky

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gaussian blur
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Re: Shouldn't be a problem
In reply to Najinsky, Apr 2, 2013

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

And you're saying this (http://support.apple.com/kb/ht4049) is wrong?:

Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

  • Apple MacBook Air SuperDrive (when connected to supported computers)

That part is wrong. The external SuperDrive only works on supported computers, which are Macs that lack an internal DVD drive, unless you patch a plist or replace a custom bridge chip. It has nothing to do with power requirements.

No it's still right, it draws 600mA (shown as Extra Operating Current), 100mA above specification. The reason the hack works is because even Macs with an internal superdrive now provide extra operating current for charging iPhone and iPads.

The external SuperDrive came out with the original MacBook Air in 2008. According to Apple's own documentation, that MacBook Air only sources 500 ma. That page at apple.com has been removed, but it's still in the Wayback Machine.

Another person tried to figure out why the external SuperDrive only worked on the MacBook Air. She tried various things, including adding additional current on both Mac and PC. It didn't help. What did work was replacing the custom bridge chip, which apparently is part of a secret handshake, with a standard bridge chip. A bit of soldering skill required, but it fixed the problem.

Later, someone figured out where the Mac checks for the drive, and by patching a plist file, the check always passes and the drive always works, regardless of which Mac, including ones that cannot source more than 500 mA.

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Najinsky
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Re: Shouldn't be a problem
In reply to gaussian blur, Apr 3, 2013

gaussian blur wrote:

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

And you're saying this (http://support.apple.com/kb/ht4049) is wrong?:

Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

  • Apple MacBook Air SuperDrive (when connected to supported computers)

That part is wrong. The external SuperDrive only works on supported computers, which are Macs that lack an internal DVD drive, unless you patch a plist or replace a custom bridge chip. It has nothing to do with power requirements.

No it's still right, it draws 600mA (shown as Extra Operating Current), 100mA above specification. The reason the hack works is because even Macs with an internal superdrive now provide extra operating current for charging iPhone and iPads.

The external SuperDrive came out with the original MacBook Air in 2008. According to Apple's own documentation, that MacBook Air only sources 500 ma. That page at apple.com has been removed, but it's still in the Wayback Machine.

Another person tried to figure out why the external SuperDrive only worked on the MacBook Air. She tried various things, including adding additional current on both Mac and PC. It didn't help. What did work was replacing the custom bridge chip, which apparently is part of a secret handshake, with a standard bridge chip. A bit of soldering skill required, but it fixed the problem.

Later, someone figured out where the Mac checks for the drive, and by patching a plist file, the check always passes and the drive always works, regardless of which Mac, including ones that cannot source more than 500 mA.

The superdrive requires 600 mA to operate reliably; presumably writing at maximum speed will be the biggest draw where this is needed. It's not uncommon for drives and devices to still operate with reduced power, but the risk is that it's operating with reduced performance/reliability.

The protocol at the time required devices to start in low power mode, 100mA and then request the additional power. As per the standard, as a USB 2 device it can request 500 mA and receives 500 mA. This is what gets shown on the system report.

The 600 mA comes by way of a protocol extension and this gets shown on the system report as Extra Operating Current. In the absence of reliable documentation I think the only way to know for sure what the MBA 2008 does is to check the system report. My money's on the 2008 MBA supplying the 600 mA EOC and the documentation being incomplete.

On the HT doc I linked to is says:

"Note: Apple computers and displays that were introduced before 2007 support only 500 mA at 5 V from their ports and do not offer additional power."

As the MBA 2008 is from 2008, I think it's a good bet it supplies the EOC.

On older Macs with the hack, I guess there's a chance it's getting by on 500 mA, perhaps accompanied with a higher occurrence of write errors at full speed.

I guess we're both a little bored today?

-Najinsky

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RustierOne
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Re: Shouldn't be a problem
In reply to Najinsky, Apr 3, 2013

Thanks for the reply. There's lots of useful information in your comment and the links. I can't say I understand some of the other posts in this thread, but I did look at the system report as suggested. For my USB devices I found the following:

  • OWC USB 3.0 750 GB, 7200 rpm - 900 ma available, 0 ma required (even when backing up)
  • Toshiba USB 2.0 750 GB 5400 rpm - 500 ma available, 2 ma required (even when backing up)
The OWC HDD is a Seagate Momentus with rated power requirement of 700 ma @ 5V. So even with the requirements for the Mercury On-the-Go drive enclosure, the total should be less than 900 ma. I've begun always connecting the USB 3.0 drive first as suggested in the link to Apple. The Toshiba drive is a self contained HDD with no separate enclosure. So I don't know its power requirements. But with USB 2.0 it should be less
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Najinsky
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Re: Shouldn't be a problem
In reply to RustierOne, Apr 3, 2013

RustierOne wrote:

Thanks for the reply. There's lots of useful information in your comment and the links. I can't say I understand some of the other posts in this thread, but I did look at the system report as suggested. For my USB devices I found the following:

  • OWC USB 3.0 750 GB, 7200 rpm - 900 ma available, 0 ma required (even when backing up)
  • Toshiba USB 2.0 750 GB 5400 rpm - 500 ma available, 2 ma required (even when backing up)

I don't understand them showing 0/2 mA required, but as USB 3 can give 900mA and USB 2 500 mA, in your setup you're good to go, no need to worry.

Your USB 2 Toshiba probably requires around 200 - 250 mA.

The OWC HDD is a Seagate Momentus with rated power requirement of 700 ma @ 5V. So even with the requirements for the Mercury On-the-Go drive enclosure, the total should be less than 900 ma. I've begun always connecting the USB 3.0 drive first as suggested in the link to Apple. The Toshiba drive is a self contained HDD with no separate enclosure. So I don't know its power requirements. But with USB 2.0 it should be less

You don't need to worry about the connection order. The comments in the Apple link only apply for an Apple device that is requesting more current than the standard, so more than 900 mA for a USB 3 device, or more than 500 mA for a USB 2 device.

Both your devices are none Apple and fall within their respective USB standards. So you can connect them in any order, plug and un-plug without rebooting (but storage needs un-mounting), and so forth, you shouldn't see any difference or have any problems.

If a non Apple device requires more current than the standard, it will usually come with a second USB cable so it can be powered by two ports, and/or an external adapter.

Technically, it may be possible for suppliers to work with Apple to have their devices request extra current. And technically it may be possible that suppliers provide their own software for PCs and maybe even Macs that achieve the same thing. But for Apple to Apple, it's handled by the protocol extension.

-Najinsky

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gaussian blur
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Re: Shouldn't be a problem
In reply to Najinsky, Apr 3, 2013

Najinsky wrote:

The superdrive requires 600 mA to operate reliably; presumably writing at maximum speed will be the biggest draw where this is needed. It's not uncommon for drives and devices to still operate with reduced power, but the risk is that it's operating with reduced performance/reliability.

The protocol at the time required devices to start in low power mode, 100mA and then request the additional power. As per the standard, as a USB 2 device it can request 500 mA and receives 500 mA. This is what gets shown on the system report.

The 600 mA comes by way of a protocol extension and this gets shown on the system report as Extra Operating Current. In the absence of reliable documentation I think the only way to know for sure what the MBA 2008 does is to check the system report. My money's on the 2008 MBA supplying the 600 mA EOC and the documentation being incomplete.

Apple states in their tech note (which I linked) that the MacBook Air 2008 only sources 500 mA.

Since the external SuperDrive worked on that machine, it only needs 500 mA. It may run a little better with 600 mA (which isn't really all that much more), but 500 mA is all that's necessary. With the plist patch, the drive will work on other Macs that only source 500 mA.

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Najinsky
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Re: Shouldn't be a problem
In reply to gaussian blur, Apr 3, 2013

gaussian blur wrote:

Najinsky wrote:

The superdrive requires 600 mA to operate reliably; presumably writing at maximum speed will be the biggest draw where this is needed. It's not uncommon for drives and devices to still operate with reduced power, but the risk is that it's operating with reduced performance/reliability.

The protocol at the time required devices to start in low power mode, 100mA and then request the additional power. As per the standard, as a USB 2 device it can request 500 mA and receives 500 mA. This is what gets shown on the system report.

The 600 mA comes by way of a protocol extension and this gets shown on the system report as Extra Operating Current. In the absence of reliable documentation I think the only way to know for sure what the MBA 2008 does is to check the system report. My money's on the 2008 MBA supplying the 600 mA EOC and the documentation being incomplete.

Apple states in their tech note (which I linked) that the MacBook Air 2008 only sources 500 mA.

Since the external SuperDrive worked on that machine, it only needs 500 mA. It may run a little better with 600 mA (which isn't really all that much more), but 500 mA is all that's necessary. With the plist patch, the drive will work on other Macs that only source 500 mA.

It's your head. Fill it with what you want.

-Najinsky

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RustierOne
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Un-mounting Drives Before Sleep-Mode
In reply to Najinsky, Apr 3, 2013

Najinsky wrote:

Both your devices are none Apple and fall within their respective USB standards. So you can connect them in any order, plug and un-plug without rebooting (but storage needs un-mounting), and so forth, you shouldn't see any difference or have any problems.

Thanks Najinski for your relies. They have fully answered my original question.

They bring up another problem I'm encountering - un-mounting all drives and partitions before entering sleep mode. When I manually enter sleep mode (closing the lid) I'm un-mounting all partitions and drives first. But sometimes when the laptop is unattended for a while it enters sleep mode without the drives/partitions being unmounted. When I wake-up the machine, there's warning message to un-mount the drives first.

Do you know of any workaround for this problem, other than just setting the time before sleep to be longer?

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Doug R
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Re: Shouldn't be a problem
In reply to Najinsky, Apr 4, 2013

I'm saying that DEC, IBM, Intel, Microsoft, NEC and Nortel did not get together and say hay the External Superdrive won't work with usb2 in usb3 lets up the curent so Apple's superdrive will work. Apple or their specific devices had nothing to do with the USB3 standard.

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noirdesir
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Re: Un-mounting Drives Before Sleep-Mode
In reply to RustierOne, Apr 4, 2013

RustierOne wrote:

They bring up another problem I'm encountering - un-mounting all drives and partitions before entering sleep mode. When I manually enter sleep mode (closing the lid) I'm un-mounting all partitions and drives first. But sometimes when the laptop is unattended for a while it enters sleep mode without the drives/partitions being unmounted. When I wake-up the machine, there's warning message to un-mount the drives first.

Do you know of any workaround for this problem, other than just setting the time before sleep to be longer?

I never had any problems of this kind, ie, putting the computer to sleep and waking it up again causing the drives to disconnect (with that warning message). While I have seen a few reports of this, the vast majority of people don't have any problems.

It could be that only some drive enclosures/drives react like this, it could be that only some Mac models react like this.

Is there a difference between bus-powered and externally powered drives for you?

(You naturally can always set your computer to never sleep on its own as a workaround.)

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Najinsky
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Re: Un-mounting Drives Before Sleep-Mode
In reply to RustierOne, Apr 4, 2013

RustierOne wrote:

Najinsky wrote:

Both your devices are none Apple and fall within their respective USB standards. So you can connect them in any order, plug and un-plug without rebooting (but storage needs un-mounting), and so forth, you shouldn't see any difference or have any problems.

Thanks Najinski for your relies. They have fully answered my original question.

They bring up another problem I'm encountering - un-mounting all drives and partitions before entering sleep mode. When I manually enter sleep mode (closing the lid) I'm un-mounting all partitions and drives first. But sometimes when the laptop is unattended for a while it enters sleep mode without the drives/partitions being unmounted. When I wake-up the machine, there's warning message to un-mount the drives first.

Do you know of any workaround for this problem, other than just setting the time before sleep to be longer?

Steve Jobs wrote an article about Adobe Flash in which he claimed it was the number one reason why Macs crashed. I haven't seen any actual figures on it, but my bet would be that the number 2 reason is USB.

It shouldn't be happening like that, but rather than spend a lot of time hunting down the problem, it might be simpler just to install Jettison from the App store for $1.99. This intercepts sleep mode, ejects any external drives, and re-mounts them on wake-up.

As to the cause of the problem:

In sleep mode, the ports should still be supplying power so the drives should remain mounted. This would be important it you were using the Power Nap feature to do Time Machine Backups while the computer sleeps.

If your rMBP is from 2012, it's worth checking it has the SMC update installed .

It's worth noting the energy saver settings (system preferences) too, specifically the check box for 'put hard disks to sleep when possible'. If it's checked, try unchecking it or vice versa.

Possibly the drives firmware has its own sleep feature and takes too long to wake when the Mac wakes, causing them to appear unmounted. If you installed any config software for the drives, try running it and seeing if there are any settings for controlling the sleep behaviour.

Until recently, my 2010 MacBook Air was running a system that had been repeatedly migrated over the years from a Mac originally running OS X 10.2 from way back when. Everything was fine except USB. Plugging in a USB devices would sometimes (it seemed completely random) kill all hardware input on the machine (keyboard/mouse/trackpad would stop working). The only options were a hard reset via the power button, or remote desktop into the machine to restart it (if I was in the middle of something and didn't want to risk a hard reset).

I've had all manner of USB devices hooked up over the years (colorimeters, serial ports, modems, network ports, hard drives, floppy drives, CD drives, cameras, robots, phones, scanning pens, drawing tablets, and probably half a dozen more I've forgotten). I assumed an old USB driver got migrated to the MBA and caused USB to randomly crash when plugging in a device. So when I got my new 13" rMBP I set it up from scratch, rather than use Migration Assistant. I also formatted the MBA's internal SDD and did a clean install on that. Neither machine has had a problem since, so I'm now fairly confident it was an old USB driver causing the issue.

The fact you reported that system report is showing 0 mA and 2 mA for your USB drives (and now this un-mounting issue) leads me to believe you may have a USB driver problem too. So I'd check the suppliers websites for all your USB devices and check for updated software, and also check if you have any old USB device related software you no longer use and see if you can uninstall it.

-Najinsky

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Najinsky
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Re: Shouldn't be a problem
In reply to Doug R, Apr 4, 2013

Doug R wrote:

I'm saying that DEC, IBM, Intel, Microsoft, NEC and Nortel did not get together and say hay the External Superdrive won't work with usb2 in usb3 lets up the curent so Apple's superdrive will work. Apple or their specific devices had nothing to do with the USB3 standard.

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Doug

No, you said:

Doug R wrote:

Najinsky wrote:

Recent Macs without built-in DVD drives; which includes the MacBook Airs, Minis, new iMacs and the retina MBPs, have extra power on the USB bus to support the the external superdrive which connects via USB but draws a bit more power.

They give more power because the specs call for it not to power a specific Apple accessory.

The Superdrive requests more power because Apple built a protocol extension in both the drive and the Macs to allow it to request more power. USB 3 is irrelevant in this, the Superdrive is a USB 2 device and can still only request 500 mA via the standard protocol, even when connected to USB 3 host.

You need to grow a set and learn to admit when you're wrong. If you want to see how, just check my posting history. I make mistakes too. The difference is when I do, I admit it, apologise and move on. That way I can learn from my mistake and avoid repeating it.

Note: Your posting history shows you to be abrupt and direct, I assume this is how you communicate so I am responding likewise. No offence intended.

-Najinsky

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Doug R
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Re: Shouldn't be a problem
In reply to Najinsky, Apr 4, 2013

I may be a bit off point but not wrong every word is true

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