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elad_sasi
Participant
July 25, 2025
Answered

copy LR preview files to another harddrive is super slow macOS

  • July 25, 2025
  • 2 replies
  • 155 views

For example, the preview file is taking forever to copy to a new hard drive in macOS

The catalogue of the file is not that big it's around 5000 photos and again I'm not talking about the smart preview. I'm talking about the preview file.

Any solution for it?

Correct answer Conrad_C

Just to be sure, do you mean the previews.lrdata file, the cache of previews?

 

The time it takes to copy depends on (A) its file size divided by (B) the real world data rate of the connection to the other hard drive, which is usually a lot slower than the internal SSD in a recent Mac. The fact that previews.lrdata is actually a package of many tiny files slows down the transfer somewhat more (more file overhead).

 

And the file size of the previews cache can become large.

So, (A) how large is the preview cache in megabytes or gigabytes?

And (B) which standard is connecting the Mac to the other hard drive? Is it…

  • USB 2
  • USB 3, 5 gigabits/sec
  • USB 3, 10 gigabits/sec
  • USB4/Thunderbolt 3/Thunderbolt 4
  • Thunderbolt 5
  • Something else (eSATA, Ethernet or wireless to NAS…)

 

For example:

I have two external SSDs connected using different standards.

My previews.lrdata file is currently 21.47GB.

I tested copying it to each SSD:

 

Standard

Transfer time

Real world data rate

Thunderbolt 3

1:42

210MB/sec

USB 3, 10Gb/sec

2:03

174MB/sec

 

So, what are your answers for (A) and (B) above?

2 replies

Conrad_C
Community Expert
Conrad_CCommunity ExpertCorrect answer
Community Expert
July 27, 2025

Just to be sure, do you mean the previews.lrdata file, the cache of previews?

 

The time it takes to copy depends on (A) its file size divided by (B) the real world data rate of the connection to the other hard drive, which is usually a lot slower than the internal SSD in a recent Mac. The fact that previews.lrdata is actually a package of many tiny files slows down the transfer somewhat more (more file overhead).

 

And the file size of the previews cache can become large.

So, (A) how large is the preview cache in megabytes or gigabytes?

And (B) which standard is connecting the Mac to the other hard drive? Is it…

  • USB 2
  • USB 3, 5 gigabits/sec
  • USB 3, 10 gigabits/sec
  • USB4/Thunderbolt 3/Thunderbolt 4
  • Thunderbolt 5
  • Something else (eSATA, Ethernet or wireless to NAS…)

 

For example:

I have two external SSDs connected using different standards.

My previews.lrdata file is currently 21.47GB.

I tested copying it to each SSD:

 

Standard

Transfer time

Real world data rate

Thunderbolt 3

1:42

210MB/sec

USB 3, 10Gb/sec

2:03

174MB/sec

 

So, what are your answers for (A) and (B) above?

JohanElzenga
Community Expert
JohanElzengaCommunity Expert
Community Expert
July 25, 2025

The previews 'file' is not really a file, but a 'package'. A package is a folder that looks like a file and can be double clicked like a file. You can see its content by right-clicking on it and choosing 'Show Package Content'. This package contains lots of small files, so copying it may indeed be relatively slow compared to if it were one big file.

 

-- Johan W. Elzenga
    E
    elad_sasiAuthor
    Participant
    July 26, 2025

    Yes, definitely everything that you wrote is correct and still my question is if there is anyway to make copy faster  ?

     

    JohanElzenga
    Community Expert
    JohanElzengaCommunity Expert
    Community Expert
    July 27, 2025
    quote

    Yes, definitely everything that you wrote is correct and still my question is if there is anyway to make copy faster  ?

     


    By @elad_sasi


    Is there a way to make copying in the MacOS Finder faster? No, I don't think so (and as this is not a Lightroom question you might ask it in an Apple forum)..

     

    -- Johan W. Elzenga
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