To wrap up the QLC saga: Crucial P1 SSDs (QLC) peaking at >50% IO usage, >1s long tail latencies, cluster fell over under load, HDDs faster (!) Samsung 970 Evo Plus SSDs (TLC) peaking at ~3% IO usage, <10ms long tail latencies, cluster *very* happy. Stay away from QLC.
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"ExplainingComputers" on youtube looked a little into this. Samsung QLC drives appear to use SLC cache of around 36GB, so up until 36GB performance was exactly the same as TLC (rather simplistic test, just transferring files), throughput then dropped to 70mb/s on QLC
The biggest problem with the Crucials isn't just performance dropping, it's that it drops to pathologic levels and long-tail latencies are absolutely ridicuous (>1 second? for an SSD?). The whole drive just stutters. Maybe Samsung QLC drives are better?
