"It Depends." If youre doing "random" writes down to the block dev, like updating a filesystem, it can be very bad. You'll end up hitting the read/update/write

"It Depends." If youre doing "random" writes down to the block dev, like updating a filesystem, it can be very bad. You'll end up hitting the read/update/write cell issues and block other concurrent access. In general I'd worry (expect total throughput to go down, and tail latency way up) around a 10-20% write:read ratio. Conversely if youre doing sane sequential writes, say log structure merges with a 64-256KB chunk size, Id expect much less impact to your read latencies.