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Author Topic: Moving Lightroom Previews from SSD to HDD  (Read 192 times)

LikesToys

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Moving Lightroom Previews from SSD to HDD
« on: December 23, 2018, 10:18:53 AM »

My Lightroom Catlg has about 200K images and the previews file was 700Gig (I will create a separate post on why that is) which consumed my entire SSD causing me to move the Catalogue to an external drive (raid 6 Thunderbolt 2) with disk throughput  at about 700MBs.  Still the SDD is noticeably faster over 1300MBs so I wanted the Catalog back on the SSD.  Here is how I accomplished moving the Previews to an external hard disk while keeping the Catalog on the SSD.

As Adobe offers no method of separating the the previews from the Catalog I had to work it out for myself using a method that would be transparent to LR and not cause problems over time.   After some research I discovered that for Mac users (and Windows via other linking methods)  can issue a Link command in the terminal window to create a "symbolic reference" to the Previews.lrdata file located at another physical location, separate from the Catalog directory / drive. This is transparent to LR and is handled by the operating system.  I understand Windows users have a similar linking facility but I don't know how to add a symbolic link to Windows so Windows users will have to Google "Symbolic Links" or Symlinks.

Mac: To create the symbolic link, use the "ln" unix command to place a symbolic link in the location that the previews.lrdata file would typically reside at in the LR Catalog, forwarding any reference to a relocated Previews.lrdata file on another drive.  In my case the new location is on a remote HDD called Areca-T2.

The basic format for the command on Mac  is: ln -s “path to previews file” “physical file location of Catalogue/Previews.lrdata”

Note that subsequently moving the Previews.lrdata file on Areca-T2  will break the link and it must be re-established.

Open a Terminal window and enter the following command - substituting your Volume and Folders. 
My command using a Catalog within a folder called "LR 7 JG_Catalog" and previews at a drive Areca-T2 Folder "LR Previews Sym Link".

ln -s /Volumes/Areca-T2/LR\ Previews\ Sym\ Link/LR\ 7\ JG\ Catalog\ Previews.lrdata     /Users/jeffg/LR\ 7\ JG_Catalog/LR\ 7\ JG\ Catalog\ Previews.lrdata

I am running LR CC 8.1 Classic and this works fine.  Note that the spaces in the folder names must be entered as per the sample above.

You may also be interested in dealing with run-away file size of the previews file in a separate post.
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howardm

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Re: Moving Lightroom Previews from SSD to HDD
« Reply #1 on: December 23, 2018, 10:46:53 AM »

Yes, that is the Unix time-honored method.  Just called a 'symbolic link' (not to be confused w/
the similar but different (and incorrect in this case) 'hard link'.

You can use quotes around the file paths to avoid using all the \\\\\\\\\\\\\  backslashes

Jeremy Roussak

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Re: Moving Lightroom Previews from SSD to HDD
« Reply #2 on: December 23, 2018, 01:45:13 PM »

Yes, that is the Unix time-honored method.  Just called a 'symbolic link' (not to be confused w/
the similar but different (and incorrect in this case) 'hard link'.

No danger of confusion in this case: the .lrdata "file" is in fact a package (folder disguised as a file), so a hard link is impossible.

Jeremy
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