iMac Pro with external hard drives


One of my biggest gripes about my iMac is the way it handles the external hard drives - you always get the spinning wheel while you’re waiting for them to come back from sleep, which makes the computer seem slow and unresponsive. Also, depending on what external drives you’re using, even starting up the computer might become a slow affair (with the LaCie Porsche Design 8 TB USB-C + USB 3.0 being the worst offender I met so far).

I am a photographer, so I need lots of storage space and continuous backups for all my photos.

What I’m wondering is if the T2 chip in the iMac Pro might help with this or not. If anyone is using one in this kind of scenario, with at least 2 external hard drives connected to the computer at all times, please let me know your thoughts!

Disable “Put hard disks to sleep when possible” if you have not done so already. That is one first step that can be done easily. ->

Probably though, the problem is not the iMac. And there is not very much Apple can do to improve the situation. External spinning drives will slow down your machine significantly. This is because hard drives act on their own. They have firmware on board with energy management. Some of them do a good job, others are bad in managing themselves and “understanding” the connected system.

If a hard drive decides to go to sleep it will go to sleep. When the Mac requests the hard drive to wake up, it needs to get spinning again and here comes the beachball.

If you have a tool to access the hard drive’s energy settings you may be able to change the settings. But that is very rare.

A different solution might be to use a tool like this:

I have not tried it but it basically prevents external spinning drives from going to sleep by constantly “updating” hidden files. Something like that should not run 24/7, I guess.

Different approaches to your problem:

  1. If possible buy yourself an external SSD drive connected via Thunderbolt/USB-C and work from there. It is like day and night in comparison to a spinning drive.

  2. If you really need 8 TB of data connected to your Mac consider using a NAS. The NAS’ system will do a way better job providing you with constant availability and a RAID will perform way better than external hard drives.

As far as I know, the T2 chip will not have any effect on the speed and sleep and wake behavior of external storage devices.


Hi Christian,

Thank you for your reply. Just checked, and the “put hard disks to sleep when possible” option was actually selected on my mac, although I’m pretty sure I had it deselected some time ago. Maybe the update to Mojave reinstated it. Anyway, I will try again without it and hopefully it will help.

You are of course right about the limitations of the mechanical drives, but it’s one thing for Finder not to be able to open that drive until it wakes up, and another for Safari not to be able to open a random web page. It’s one thing for the boot time to be affected if the OS is installed on the spinning drive, and another when the OS is installed on a SSD and the spinning drive contains just photos. The way I see it, this is more about OS than the drives themselves.

I already have an external SSD connected via USB-C and it works great, but unfortunately doesn’t cover my whole storage needs. I also tried to go the NAS route, but the performance was really disappointing.

There are a lot of reasons that can cause this behavior. One example is that a website uses a certain font. Safari looks up the installed fonts on your system and loads the requested font. If you have fonts that are located on an external drive this will lead to the external hard drive spinning up. There may be 100 further reasons for this behavior.

One possible scenario that can lead to your issue: If you have Spotlight enabled to include the content of the external hard drive the system will every once in a while try to access it in order to keep the Spotlight index up to date. There are many different reasons that can cause your issue. Finding the culprit is not easy and even if you do there is not always a solution that stops the slowdown from happening.

I have to admit that this topic is not an easy one. If you have a good NAS that contains a RAID connected to your Mac using a very good WiFi connection or even better an Ethernet connection you really should not have performance issues. With the release of the new Mac Mini, we even see 10Gbe solutions on a “little” Mac. A connection like that is crazy fast.

Be it as it may, if you do not want to be slowed down using an external USB spinning hard drive connected to your computer you will have to make sure that the hard drive keeps spinning as long as you use your system. Otherwise, you will keep running into slowdowns. You will experience the same problems with a PC running Windows when having a spinning hard drive connected via USB. This is no Mac-related issue. I do not know any operating system that has no issues with external spinning hard drives connected via USB.

My solution is to only have SSDs connected to my iMac via Thunderbolt. When I am actively working on stuff that needs high data throughputs like editing video, they are located on the SSD. In the long run, everything gets transferred to my NAS and I am fine accessing it even via WiFi (file transfers between 30 to 50 megabytes per second).

Because of the fact that external spinning hard drives are on the way out, I do not expect an improvement of this issue. Everything goes to SSDs for fast local data storage, NAS storage for high amounts of data in your LAN and of course WAN cloud solutions.


For photos at work I use a MacBook Pro connected to 8 hard drives across two enclosures. The drives are striped together (RAID 5) with SoftRAID, and the boxes (I’ve used OWC’s Thunderbays, but these are slightly cheaper Akitios) are connected to the laptop via TB3 connections.

No spin-up of the drives, or delays accessing them. SoftRAID with that number of disks actually gives me SSD-like speeds (460 MB/s up, 700 MB/s down), as well as gobs of storage.

SoftRAID is slated to offer a RAID 6 next year; I’ll migrate this array and another back up to that safer arrangement. No migration path, though, so I’ll need to reset the arrays and recopy the data.


Sounds like a good option in terms of performance, although probbaly too expensive for me for the moment. :frowning:

One possible scenario that can lead to your issue: If you have Spotlight enabled to include the content of the external hard drive the system will every once in a while try to access it in order to keep the Spotlight index up to date.

We’re talking about booting times, not sure how keeping the Spotlight up to date would impact that.

If you have fonts that are located on an external drive this will lead to the external hard drive spinning up.

Not really, the whole OS is installed on the internal SSD, the external hard drives only contain media.

The behaviour I’m describing is more like the whole system is freezing until the external drives wake up, regardless what information exists or not on them. The same things happens even with a freshly formatted external drive. That’s why I thought this is related with the way MacOS works and that it may be impacted by the T2 chip.

You are 100% right. There is absolutely nothing Spotlight indexing has to do with boot time. I misread your mentioned sentence (I have overlooked the “booting” part for some reason). I am sorry. Spotlight indexing will only affect the system’s performance when the system is up and running and if the external drive is part of the places where Spotlight does its thing.

If this is how your drives interact with MacOS then there is nothing you can do about it other than keep the external drives spinning so that they do not need to spin up and therefore respond more quickly when accessed or being checked by the system or other applications. A first step is the mentioned system energy setting. A second step might be a tool that is accessing the drive regularly in order to prevent the drive from sleeping.

If it happens with a freshly formatted drive then it is the way your MacOS installation works. True. The T2 chip will not do any good in this case. The chip is designed to interact with the internal components of new Macs in order to provide security features and to a lesser degree to take workload from the CPU for specific tasks. More at and

So, my final words on this (I promise to be quiet after that :slight_smile:):

A trusty hard drive will slow down any system up to a temporary halt if it has stopped spinning and it is being accessed in that state. There are a lot of scenarios and operations of the OS and of applications that will access external drives directly or indirectly (a simple enumeration of connected USB devices leads to a drive spinning up). If something wants a response from a sleeping hard drive it will only get the response after the hard drive has recovered from sleeping. And this takes time.

If you like to do so you could provide Apple with your feedback at with the request to improve the situation.