Hi, On Tue, Feb 06, 2024 at 11:03:03AM +0100, Basti wrote: > If you use mdadm for RAID you can mark the slower disk as 'write-mostly' to > get more read speed.
Both (MD) RAID-1 and RAID-10 will work this out by themselves, by the way, and tend to read from the fastest device. I have benchmarked this. With very fast enterprise NVMe as the faster device and consumer SATA SSD as the slower "write-mostly", I wasn't able to detect much benefit from using "write-mostly", i.e. MD already chose to read mostly from the NVMe. When pairing any kind of SSD with HDD, the difference was more dramatic and "write-mostly" did have noticeable beneficial effect, though not huge. Again, MD by itself chose to read from the SSD even without "write-mostly". I hypothesise that this is because MD picks the mirror device with the lowest outstanding request count, and that is often going to be the flash-based device. Thanks, Andy -- https://bitfolk.com/ -- No-nonsense VPS hosting
