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Cache Full: expected behavior?

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What is the expected behavior of the server when my cache disc becomes full during file operations? When I am transferring a large file (or a folder of smaller files) to the server in one operation (from Windows), if the cache becomes full I get a "disk full" error from windows and the operation is canceled. I have to invoke the Mover function to clear space in the cache in order to proceed. This limits the file sizes that I can transfer to how much free space I can clear on my cache. I would have hoped that instead of failing the UnRAID server just started writing to storage disc instead of cache but that is not what it currently does. Is there any option to change that behavior?

Solved by trurl

Mover runs on schedule. Default is once-per-day in the middle of the night.

It is impossible to move from fast cache to slow array as fast as you can write to cache. If you try to move while still writing, it is even worse.

If you need to transfer more at one time than cache can hold, don't cache.

You can make writing directly to the array somewhat faster with "turbo".

https://docs.unraid.net/unraid-os/using-unraid-to/manage-storage/array/overview/#array-write-modes

For initial data load, you can unassign parity to make array writes even faster, then build parity after.

  • Solution
2 hours ago, zero_koop said:

I would have hoped that instead of failing the UnRAID server just started writing to storage disc instead of cache but that is not what it currently does. Is there any option to change that behavior?

Whether or not a user share will overflow from cache to array depends on the settings for cache Minimum Free and for Minimum Free for the user share.

https://docs.unraid.net/unraid-os/using-unraid-to/manage-storage/cache-pools/#minimum-free-space-for-a-cache-pool

https://docs.unraid.net/unraid-os/using-unraid-to/manage-storage/shares/#minimum-free-space

3 hours ago, zero_koop said:

I would have hoped that instead of failing the UnRAID server just started writing to storage disc instead of cache but that is not what it currently does. Is there any option to change that behavior?

As mentioned it's the min free space that needs to be set properly on the shares so that it does, to about twice the max file size you might expect to write to them.

Edited by Kilrah

  • Author

Ok thank you. Sounds like I need to adjust that "min free space" setting. I came across that idea when searching the web but I'm having trouble wrapping my head around what that means and why it would affect the scenario I'm describing but I'll research it some more and make the change once I grasp it.

6 hours ago, trurl said:

If you want more specific advice

Attach Diagnostics ZIP to your NEXT post in this thread.

5 hours ago, zero_koop said:

Ok thank you. Sounds like I need to adjust that "min free space" setting. I came across that idea when searching the web but I'm having trouble wrapping my head around what that means and why it would affect the scenario I'm describing but I'll research it some more and make the change once I grasp it.

Note that there is also a Minimum Free Space setting for the 'cache' pool that is independent of the setting at the User Share level. You definitely want this set to stop the pool filling up too much.

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