On Wed, Jul 30, 2025 at 01:47:53PM +0200, Greg wrote: > Hi there, > > I have a "server" running 24/7 with a lot of RAM. I would like to speed up > disk system by giving much higher priority to reads and delaying writes. > > YES, I KNOW THE RISK! > > As I understand, there are two things to tune: > > 1. I/O Scheduler. The default is mq-deadline. Let say I have md_raid array > /dev/md0 consisting of /dev/sd[ab]. Should I keep it for both, md0 and > physical disks? Which I/O scheduler parameters should I change in case of > md0 and which in case of sd[ab]? > > 2. Kernel runtime parameters. As I understand I should focus on vm.dirty_* > parameters. My Idea is to set vm.dirty_ratio=70 and > vm.dirty_expire_centisecs to something like 10 to 60min. Should I change > anything else? There is more to it: an application can explicitly request syncs to disc. To tackle this, cf the package eatmydata (typically you use this one when building throwaway VM/container images and want things to be fast, not safe: you just rebuild anyway if things go south). > PS. Among others, I'm trying to learn something about Linux caching. So > please stick to above questions. Sorry for the slight tangent, but fsync, O_DATASYNC and friends might trip you up, so a heads-up seemed to be in order. Cheers -- t
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