windows user, using latest rclone v1.5.1.0 and winfsp v1.6
i am trying to use a ramdrive for the vfs cache of a limited size.
i keep getting errors such as
2020/03/24 14:25:47 ERROR : IO error: write r:\cache\vfs\wasabieast2\en07\test\50files\FileGen 1857341572.bin: There is not enough space on the disk.
i need a flag to set the absolute total size of the cache in such as 100MB.
then no matter what, rclone will not fail when the 100MB is reached.
any suggestions?
Pretty sure you can't hard-limit the VFS cache currently. The max-size is actually a target-size and not a hard-limit. It can and will expand beyond this - but periodically be pruned down to the target size. (how often is up to you - via a flag)
It will expand as much as it needs (temporarily) to accommodate the files that are currently writing and/or not yet fully uploaded (even if this brings it temporarily over the target maximum). Usually not a problem - but on a RAM-disk it indeed might be due to very limited size.
I'm pretty sure a new flag would need to be implemented for this - to perhaps delay any transfers that could not be guaranteed to fit within the cache absolute-limit. @ncw how feasible is this you think?
Sidenote: If you are into this sort of tiered-storage stuff I highly recommend looking into Primocache. It is easily the best user-customizable solution that exists currently. HDD's, SSDs, RAM, - tier them as you wish and let them fly 
That said though - HDDs don't really wear down from writes like SSDs do so they make excellent cache-drives. HDD failure is kind of random except that you want to keep them as temperature-stable as feasible according to statistical data from major datacenter sources. They means basically "any minimal airflow" is great. Over-cooling might actually be detrimental, but leaving them without any airflow at all is bad. I run all my HDDs in bays with the fans set to the minimal they will spin at (inaudible) and their temperature-change over time is very slow, which is the most ideal scenario according to the best science on the topic.
TLDR: Don't be afraid to use a HDD as a cache-disk. Even an old one will be faster than your gigabit and not be a bottleneck, and you probably aren't going to "wear it out" by writing to it.
Actually - the best advice is probably not not spin it down in idle. load/unload cycles on the read heads is a significant statistical factor in failure. Keep it with some airflow and don't let it spin up/down all the time and your HDD will last maximally.