Any suggestions on mixing ssd and hdd in btrfs

[rustybird]

@logoerthiner

In LVM I was able to utilize SSD speed while keeping my big private disk vm on hdd, by making a dedicated thin pool in SSD, add this pool to qubes os and then cloning my template vm onto the new pool. In this way I can access the root.img of each vm from SSD

What are the counterpart in btrfs?

You could similarly create an independent Btrfs filesystem on the SSD (or rather, on a new LUKS device on the SSD), set it up to be automounted, and add another file-reflink Qubes OS storage pool somewhere on the mountpoint.

@solene

I wouldn’t recommend mixing a ssd and a hard drive in a same pool.

+1

@logoerthiner

In btrfs when I specify “DUP” profile, the one gets read is determined by pid parity (BTRFS raid-1: which device gets the reads? - Stack Overflow). I am not sure whether the storage driver in qubes os always picking the ssd or hdd.

This is just a guess but maybe Btrfs would decide based on whatever happens to be the PID of (one of) the kernel thread(s) servicing the xen-blkback device corresponding to the VM volume?