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User profile for user: Ian R. Brown
Ian R. Brown Author
User level: Level 7
22,596 points

Strange export times when booting from iMac HDD or bootable USB 3.0 SSD

I have been doing some tests to find the most efficient way of using FCP as I wanted to discover the difference between working on my 2017 Fusion drive iMac or booting from a 275GB Crucial USB 3.0 SSD.


To begin with I tested the normally booted iMac and then the iMac booted from the USB SSD with Geekbench 5 and the results were virtually identical . . . if anything the Crucial SSD was a tad faster.


I then made a 6 minute 4K video with various effects including PIP.


Initially the Library was stored on a 9 year old Toshiba 1TB portable USB 3.0 HDD.


Exporting from the iMac took 4m 52 seconds.


Exporting from the booted Crucial took nearly 2 minutes longer for the QT video at the end to popup.


The weird thing is that they were identical all the way up to 95% but the final bit to open the video in QT took under 20 seconds when booted into the Mac but nearly 2 minutes when booted into the SSD.


Why?


Next I wondered how much I was being slowed down by having the Library on an old spinning USB so I copied it to the desktop of the iMac and also to the desktop of the bootable SSD.


To my surprise there was no significant difference in export times, the results being identical to the above together with the grossly extended time required for the QT movie to open on the Crucial SSD.


So I can't detect any speed difference in editing wherever I put the Library or whatever I boot into but I do get that weird final opening delay when booting into the SSD.


Any comments or ideas why I get these results?

iMac 27″ 5K

Posted on Apr 30, 2023 6:14 AM

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User profile for user: Luis Sequeira1
Luis Sequeira1
User level: Level 9
68,038 points

Posted on May 2, 2023 5:03 AM

Ian R. Brown wrote:

Just discovered that the progress bar only goes up to 95% when the export is set to open QT Player on completion. Set it to just Save and it goes up to 100%. That's the way it is.

I have also done further tests exporting a 4 minute 4K movie and both the iMac booted normally and the iMac booted via the USB 3.0 SSD produced identical times of 3m 22s.

I am gobsmacked as to why a USB 3.0 bottleneck can allow this.


I think that the short explanation is that the most important factor in doing a video encoding is the processor speed, and not the drive speed. Your drive can perhaps support a data rate of 150MBps; and your SSD, say, 1500MBps (these are just examples, either could be slower or faster than these numbers).

How much of these 3m 22s is spent loading and writing the media back to disk? A small percentage.

It is much like you won't see a huge decrease in your home electricity bill by switching to more efficient lamps. Why? Because most of the cost is not lighting, but your appliances, heating, perhaps charging your car. A 50% improvement on a 1% part of the cost is only 0.5% of the total



Geekbench scores identical as well!

Again, these test mostly the CPU, and that does not change.

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User profile for user: Luis Sequeira1
Luis Sequeira1
User level: Level 9
68,038 points

May 2, 2023 5:03 AM in response to Ian R. Brown

Ian R. Brown wrote:

Just discovered that the progress bar only goes up to 95% when the export is set to open QT Player on completion. Set it to just Save and it goes up to 100%. That's the way it is.

I have also done further tests exporting a 4 minute 4K movie and both the iMac booted normally and the iMac booted via the USB 3.0 SSD produced identical times of 3m 22s.

I am gobsmacked as to why a USB 3.0 bottleneck can allow this.


I think that the short explanation is that the most important factor in doing a video encoding is the processor speed, and not the drive speed. Your drive can perhaps support a data rate of 150MBps; and your SSD, say, 1500MBps (these are just examples, either could be slower or faster than these numbers).

How much of these 3m 22s is spent loading and writing the media back to disk? A small percentage.

It is much like you won't see a huge decrease in your home electricity bill by switching to more efficient lamps. Why? Because most of the cost is not lighting, but your appliances, heating, perhaps charging your car. A 50% improvement on a 1% part of the cost is only 0.5% of the total



Geekbench scores identical as well!

Again, these test mostly the CPU, and that does not change.

Reply
User profile for user: Ian R. Brown
Ian R. Brown Author
User level: Level 7
22,596 points

May 2, 2023 4:50 AM in response to Ian R. Brown

Just discovered that the progress bar only goes up to 95% when the export is set to open QT Player on completion. Set it to just Save and it goes up to 100%. That's the way it is.


I have also done further tests exporting a 4 minute 4K movie and both the iMac booted normally and the iMac booted via the USB 3.0 SSD produced identical times of 3m 22s.


I am gobsmacked as to why a USB 3.0 bottleneck can allow this.


Geekbench scores identical as well!

Reply

Strange export times when booting from iMac HDD or bootable USB 3.0 SSD

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