iMac External Drive Speed (vs Lightroom)

I recently upgraded to a new Late 2015 i7 Retina iMac (8GB, 500GB SSD, 4GB m395x video) and also bought Lightroom 6, and a new 4TB Seagate USB 3.0 "Backup Plus Fast" external hard drive.

The external drive is a single, portable, raided device that offers great speeds, about 4x faster than most external USB drives. I get a 240 MB/s read and write bench and a 1GB file can copy to my drive in a few seconds which beats my WD My Passport Ultra 2TB USB 3 drive by a fair margin (about 4x faster as mentioned).

I have all my pics and LR catalogue on the Seagate drive, and I notice when LR is open, the external drive's speed drops by about 75% (about 50 MB/s reads/writes), even if there is nothing apparently going on in LR. I check Activity Monitor and it shows no CPU usage or disk reads or writes. Even my WD external drive will drop in speeds from about 80 MB/s to about 30 MB/s.

A file transfer is also about 4x slower for each drive. A 1GB file transfer now would take 10-15 seconds on the Seagate.

When I close LR, this persists for up to 5 minutes after, the slow speeds persist, then they return back to normal. This is repeatable.

I've tried running only 1 drive plugged into the USB on the iMac, same issue though. What could LR possibly be doing to have this happen?! I initially thought it was reading catalogues or something but again, the Disk Activity in Activity Monitor is basically nil. I'm at a complete loss!

Btw, I have Photoshop CC and it's fine. I can open 1GB PSD files from the same Seagate drive, and no issue at all.

LR might be indexing or cataloging the drive?

I wonder if it's best to leave LR open overnight or something. The weird thing is that Activity Monitor shows little hdd read/write activity. I also think my other external drive slows down too and it's got nothing on it involving LR

It turns out it's something to do with how the drive is reading the previews file "Lightroom Catalog Previews.lrdata" . I moved it off the external and now all is fine.
Just the process of deleting that file off the drive took 15 mins. I wonder why?!
Copying that file took nearly 2 hrs instead of abut 10 seconds as it should for a 2GB file.
I don't get it!

drisley wrote in post #17894358
It turns out it's something to do with how the drive is reading the previews file "Lightroom Catalog Previews.lrdata" . I moved it off the external and now all is fine.
Just the process of deleting that file off the drive took 15 mins. I wonder why?!
Copying that file took nearly 2 hrs instead of abut 10 seconds as it should for a 2GB file.
I don't get it!

I'm guessing there's many, many thousands of files, so each delete requires commands to delete the file, then get a 'success' message, then delete the directory entry, then get 'success', etc.

I know when scanning, those small files take a ton of time, same for backup programs.

Well, I copied the preview and catalogue files back to the external drive, then opened in LR and had it do an "integrity check" of the catalogue. Now all is good! *fingers crossed*
It appears perhaps the lrdata file was corrupt!

Speeds are nice and fast for an external and LR opens and closes down now instantly.

Spoke too soon, the problem seems to have returned again, directly related to the lrdata file.

You might have failing ram or power supply...

Well, it's a brand new iMac so I doubt that. I guess that could happen. Everything else is fine, just LR has issues with that lrcat file.

I notice the issue is with the LR Preview Cache. When I open the catalog settings, the TOTAL SIZE is a spinning circle for 10 mins. Once it completes then it's fine.

Same on my old PC, LR will show a spinning circle for TOTAL SIZE for the Preview Cache, and it will lock up for an hour or more before it actually gives a size in GB.

So I see issues it on both a PC and Mac.

Sounds to me as if you have an issue with the previews, and they are rebuilding every time you open LR. I often get the power go off here and so the computer crashes. This will often cause LR to fail to open correctly, and it shuts back down, and then has to rebuild the previews when you start it again. Sometimes it is so bad that I have to delete the preview folders completely in order to get LR to restart.

Alan

Well the thing is, if I try to copy the preview file over to my main ssd, even with LR closed, it sometimes hiccups. I wonder if it's the external drive because it's a raid drive? Very inconsistent though.

Have you optimized the catalog? And Adobe's advice to have all the catalog, cache, etc files in the same location? (I haven't re-read the thread to see if you've done this... )

I will try optimizing... it's a brand new computer and brand new hdd, so I didn't think that would be necessary.
The weird thing is, even if LR is closed, and I use FINDER to drag the file off the drive, it bogs the drive down to about 1/10th its normal speed.... sometimes. Not always. Something bizarre going on.