Just a short note here. Many Linux distributions by default uses the mq-deadline scheduler for HDDs. I’ve just found out that this scheduler only gained support for I/O classes in Linux 5.14 (August 2021), so this patch won’t improve anything immediately for users of e.g. some long-term supported distributions that use older kernels (like Debian Bullseye—thankfully, Bookworm is just around the corner!), or users of NASes that don’t get their kernels updated. It may be useful for node operators to explicitly check whether their I/O scheduler supports the Idle class, and maybe update the kernel, maybe switch to BFQ, which does support I/O classes.
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