Last night, I updated to a much newer version of the Mist Ethereum wallet than when I last used it (0.2.6 to 0.8.9) about 1 year ago, and from everything I've read on DAG size, it's using far more space than it should be (which is why I was never able to run it off my SSD previously - it would eat 10+ GB and get too close to the 90% mark of my puny 128GB boot drive, and I'd have to cancel it).
Last night, I finally figured out 'mklink', and the DAG is happily syncing away, thinking it's in %appdata% when it's actually being pointed to a spot on my spinning disk drive.
The wallet app seems fine with this. It recognized right where I was as far as the last time I synced the DAG, and proceeded from there (I had just under 1M blocks to go, as of 4 hours ago). I made a note of how much free space I had when I began the sync process, so I'd know how much it was taking up.
Fast forward to now: When I wrote it down, I had 360GB free on the HDD I'm using. As of now (75.7% sync), I'm down to 337GB free, or around 23GB of DAG. Accordingly, the 'chaindata' folder it is syncing to is exactly 30GB at time of writing (7GB having been downloaded 1 year or more ago).
This is the same behavior I was seeing before relocating the DAG using mklink, so I don't believe that has a anything to do with it - in fact, I haven't ever had a fully synced DAG on my PC (only my mining rig, over a year ago when it was much smaller), because it would never fit on my paltry remaining SSD space.
If it helps diagnostically, the 'chaindata' dir contains 16,060 items (and counting), each approx. 2MB, and starting chronologically with 047061.LDB (in 2016), up to the present 191120.LDB (quickly being usurped by newer files).
Thanks very much,
Edit: Sync now 86% complete, /chaindata up to 36GB
Edit2: Sync now 98% complete, /chaindata up to 43GB