Measuring the WAL vs DB Performance Gap on Ceph USB OSDs
Nine of my fifteen Ceph OSDs use WAL-only acceleration while six use DB. I set out to measure the performance gap and discovered the real story isn't WAL vs DB — it's the USB 3.0 hardware ceiling that dominates everything. The matched-hardware comparison shows DB is 5-15% faster on reads, not the 32% that naive cross-node testing suggested.
Linux Disk I/O Performance in the Homelab
I swapped my physical disks around in my low-end testing hardware cluster. I have a mixture of soldered to the motherboard eMMC and an external USB3 Thumbdrive serving for a root file systems and external /usr volumes now. I would like a quick performance check on reading and writing to those file systems. I also don’t want to setup a huge performance benchmark suite or additional tooling. I just want some quick results at this point.
My basic question is what did I lose in this decision to break out my /usr out to an external USB3 drive. How much performance did I lose?