All Posts by Date or last 15, 30, 90 or 180 days.
also by Lloyd: diglloyd.com photography and WindInMyFace.com
Thank you for purchasing through links and ads on this site.
OWC / MacSales.com...
diglloyd Deal Finder...
Buy other stuff at Amazon.com...
Get up to 16x more storage and 2x the speeds of the original drive
Handpicked deals...
$2998 $2498
SAVE $500

$350 $280
SAVE $70

$1598 $998
SAVE $600

$399 $329
SAVE $70

$1069 $869
SAVE $200

$1299 $899
SAVE $400

$1499 $999
SAVE $500

$1499 $1019
SAVE $480

$1799 $1349
SAVE $450

$3698 $2998
SAVE $700

$2397 $1897
SAVE $500

$1199 $898
SAVE $301

$1299 $1169
SAVE $130

$4499 $3999
SAVE $500

$1399 $1099
SAVE $300

$1499 $1299
SAVE $200

$4499 $3149
SAVE $1350

$2299 $1599
SAVE $700

$1799 $1349
SAVE $450

$2998 $2498
SAVE $500

$2199 $1999
SAVE $200

$430 $230
SAVE $200

$3399 $2199
SAVE $1200

$6299 $3599
SAVE $2700

$400 $280
SAVE $120

$1499 $1019
SAVE $480

$1279 $719
SAVE $560

$1699 $1549
SAVE $150

An eGPU is Useless for Photoshop and Lightroom Unless...

The 2018 Mac mini has four Thunderbolt 3 ports with two busses. The 2019 iMac 5K has only a single Thunderbolt 3 bus, thus half the bandwidth—hobbled, more on that below.

David Cwrites:

You know about eGPUs (and similar) things, right?

It seems to me having only a single Thunderbolt 3 bus is a handicap if you plan to run external storage, e.g. SSDs with an eGPU. maybe the render is so fast it doesn’t matter or maybe it’s fine with one GPU because you need only one data channel?

The eGPU route does seem a way around a non-replaceable graphics card, but I don’t know if using one is generic or can only be whatever specific model(s) the OS supports, i.e. whatever Apple deigns to allow.

The 2018 Mac mini has four Thunderbolt 3 ports but I am unable to find out how many buses they run on. I guess two Thunderbolt 3 ports on the same bus would be slower than on two separate buses, but that also assumes a single bus isn’t fast enough two handle two thunderbolt 3 devices at full speed. Ignorance on display here…

DIGLLOYD: the 2018 Mac mini has four Thunderbolt 3 ports on two busses, so it has double the bandwidth of the 2019 iMac 5K.

It’s a serious handicap to have only one bus; see Understanding Thunderbolt 3 Bandwidth. The 'hit' is severe when an external 5K or 4K display is used because a big chunk of available bandwidth is sucked up for the display. That is why the 2019 iMac 5K is a flawed machine and should be avoided for anyone contemplating an external 5K or 4K display.

An eGPU is 100% useless for Photoshop and LR unless it is driving main screen — those programs use only one GPU, the one for the main display. Think iMac 5K, iMac Pro, all laptops — for all of these, unless the built-in display is configured as the secondary display, the eGPU does nothing for Photoshop and Lightroom — they won’t use it. Actually, I’m not sure an eGPU is used by Photoshop and/or Lightroom even if the built-in display is the secondary display. Maybe readers can confirm/refute that.

When testing the 2018 Mac mini, I discovered this issue. The reason I did not post any eGPU benchmarks for the 2018 Mac mini is that I had trouble getting the eGPU to drive the screen reliably. So if the screen is driven by the built-in graphics, the eGPU is 100% useless for Photoshop and Lightroom — it goes unused.

From Adobe: GPU troubleshooting and FAQ:

Lightroom CC/Lightroom 6 currently doesn't take advantage of more than one graphics processor. Using two video adapters does not enhance performance.

From Photoshop graphics processor (GPU) card FAQ:

Lightroom CC/Lightroom 6 currently doesn't take advantage of more than one graphics processor. Using two video adapters does not enhance performance.

The unstated huge downside left unsaid in both of above quotes is that using built-in graphics for the built-in display can mean the eGPU goes unused. As the built-in display cannot be driven by an eGPU, that in turn implies that even if Photoshop/LR will use the GPU for the main screen, the user must then force the built-in display to be the secondary display (if indeed that works).

See also: Apple: https://support.apple.com/en-us/HT208544 and


Save the tax, we pay you back, instantly!
View all handpicked deals...

Beats by Dr. Dre Studio3 Wireless Bluetooth Headphones (76ers Blue / NBA Collection)
$350 $280
SAVE $70

diglloyd.com | Terms of Use | PRIVACY POLICY
Contact | About Lloyd Chambers | Consulting | Photo Tours
Mailing Lists | RSS Feeds | Twitter
Copyright © 2019 diglloyd Inc, all rights reserved.
Display info: __RETINA_INFO_STATUS__