I suspect that simply adding the bcache module to the kernel is not all that would be involved or it would probably already have happened.    For instance how would it interact with the Unraid User Share system?  
 

Having said that if such issues could be resolved it might be an attractive feature and at the very least it would replace the need for the current Use Cache=Yes option on User Shares.

hope this function add to urnaid，cache  setting up cache on dir is improper，not flexible enough

any updates about this ask in 2024?

I google this at least twice a year to see if there’s been any updates. 

On 10/1/2023 at 7:42 AM, itimpi said:

I suspect that simply adding the bcache module to the kernel is not all that would be involved or it would probably already have happened.    For instance how would it interact with the Unraid User Share system?  
 

Having said that if such issues could be resolved it might be an attractive feature and at the very least it would replace the need for the current Use Cache=Yes option on User Shares.

Unraid 7.0 kernel has the bcache-linux module. What is missing is unraid web interface hooks to detect and handle the configuration of bcache disks (its similar to setting up a disk partition format dance).

1. /dev/sda needs to be bcache formatted via make-bcache command.

2. Now that /dev/bcache0 exists, unraid needs to allow us to put encryption or a partition on top. In other words unraid needs to threat /dev/bcacheN as it does for /dev/sdN in the current state of affairs.

I haven't bruteforced since I don't have a spare license and all my USB disks all have undergone a trial already but I did see I was able to create a /dev/bcache0 device on my unraid because the kernel has the module it needs - i just needed to drop the binaries for the userspace tooling that talks to the kernel and go to town.

https://github.com/TheLinuxGuy/ugreen-nas/blob/725850e877731aa475300b3eacfdd7f853640b8a/bcache-cheatsheet.md?plain=1#L53

On 7/11/2025 at 11:16 PM, TheLinuxGuy said:

Unraid 7.0 kernel has the bcache-linux module. What is missing is unraid web interface hooks to detect and handle the configuration of bcache disks (its similar to setting up a disk partition format dance).

1. /dev/sda needs to be bcache formatted via make-bcache command.

2. Now that /dev/bcache0 exists, unraid needs to allow us to put encryption or a partition on top. In other words unraid needs to threat /dev/bcacheN as it does for /dev/sdN in the current state of affairs.

I haven't bruteforced since I don't have a spare license and all my USB disks all have undergone a trial already but I did see I was able to create a /dev/bcache0 device on my unraid because the kernel has the module it needs - i just needed to drop the binaries for the userspace tooling that talks to the kernel and go to town.

https://github.com/TheLinuxGuy/ugreen-nas/blob/725850e877731aa475300b3eacfdd7f853640b8a/bcache-cheatsheet.md?plain=1#L53

Ohhh, if this gets added it would be fantastic for people who don't use ZFS. Too bad this wasn't around before I rebuilt my entire server. Still going to be keeping my eye on it.

interesting topic.

I don't have need for bcache for the array. I'm happy with it as it is. Despite of the downsides the versatility it provides in the ability to mix disks is what made me choose unraid in the first place.

But i have a need for a vm to have a large and fast volume. Too large to hold it on a ssd and too fast to rely only on hdd. It doesn't need to on the array.

How could i setup such a volume ?

I was thinking about lvm volume with bcache or another type of cache (completly outside of the array). The glitch is i have room for another hdd but not for a ssd. Could i use a vdisk on a existing ssd to act as cache for a lvm volume on a new hdd?