I keep rebuilding thumbs, done this for a bout a week making sure everything is built.
Why do thumbs get erased? One thought...I updated my DSM on Synology today and MC probably noted the NAS was offline
This is almost certainly what is happening. To explain something... You don't seem to understand what MC is doing when it is building thumbnails. That's okay, as it is somewhat esoteric and nerdy!
MC cannot use the thumbnail JPG files directly on disk for display. If it did, it would NEVER be able to perform well when showing thousands of assets, or even probably a few hundred. If you don't believe me, try this:
1. Make a folder in Windows, and copy a few image files into it.
2. Switch the View in Windows Explorer to Large or Extra Large Icons mode.
3. Now, copy 3-4 thousand files into the folder. You can do this pretty easily from MC if you have your photos imported, just select a huge swath of them and copy them into the folder.
4. Now, open the folder in Windows Explorer, and try to change the sorting.
5. Watch it hang for minutes at a time.
On my system at home, if I change the sorting of my Photostream folder (which has a few thousand 4-8 megapixel JPGs all dumped into the root folder) Windows Explorer usually takes 10-20
minutes to refresh the view.
That's because for all changes, it has to read the files off of disk, generate a screen-optimized thumbnail, and then do a complex sorting algorithm on top of it. This is just hard, and limited heavily by disk throughput. So, MC doesn't do that. It can't because it is often asked to show many thousands of photos on the screen at one time. Windows Explorer can usually safely assume a single folder won't contain thousands of images.
What MC is doing when it is building thumbnails is it is building a highly-optimized for on-screen display cache of the thumbnails, in a variety of sizes, so that it can cache the part of it needed in RAM, and show the artwork for thousands of files all at once and do so
fast. This is the exact same strategy used by everything from Adobe Bridge and Lightroom to iTunes to iPhoto. Basically any application that shows a bunch of artwork on screen and needs to scroll them around needs to be able to build an optimized cache of the artwork. It cannot read them on the fly from disk or else it will drag horribly when you try to scroll.
If your thumbnails are being lost/rebuilt regularly, then performance in MC is going to be
terrible whenever this happens.
I'm not clear on exactly when MC loses thumbnails. I think we need someone from JRiver to respond. However, I know offline disks can cause it. I have a lot of assets in my main home Library that are on external disks that are typically disconnected and on a shelf. I use them for "cold storage" of files I want to keep, but which I don't need online all the time (old episodes of shows I've already watched, movies, etc). As soon as I disconnect one of these, it loses all the thumbnails for the entire disk, if the view showing these files is active at the time.
Then, when I plug the drive back in, MC has to rebuild the thumbnail cache for those disks, and the performance of the views showing those files suffers until the process is completed, as expected. But, this isn't something that happens to me regularly (and my main Media Library volumes don't go offline, just these external "cold storage" disks). Under what circumstances do these thumbnails get lost?
Perhaps MC could be tweaked somehow to make it work better with your network volume if it is disconnecting all the time, or maybe something else is going on?
