"Numbers everyone should know",
courtesy of Jeff Dean:
* L1 cache reference 0.5 ns
* Branch mispredict 5 ns
* L2 cache reference 7 ns
* Mutex lock/unlock 100 ns
* Main memory reference 100 ns
* Compress 1K bytes with Zippy 10,000 ns
* Send 2K bytes over 1 Gbps network 20,000 ns
* Read 1 MB sequentially from memory 250,000 ns
* Round trip within same datacenter 500,000 ns
* Disk seek 10,000,000 ns
* Read 1 MB sequentially from network 10,000,000 ns
* Read 1 MB sequentially from disk 30,000,000 ns
* Send packet CA->Netherlands->CA 150,000,000 ns
Similarly (and courtesy of Jeff Dean and Sean Quinlan), "The Joys of Real Hardware" lists the typical problems a new cluster will experience in its first year:
- ~0.5 overheating (power down most machines in <5 mins, ~1-2 days to recover)
- ~1 PDU failure (~500-1000 machines suddenly disappear, ~6 hours to come back)
- ~1 rack-move (plenty of warning, ~500-1000 machines powered down, ~6 hours)
- ~1 network rewiring (rolling ~5% of machines down over 2-day span)
- ~20 rack failures (40-80 machines instantly disappear, 1-6 hours to get back)
- ~5 racks go wonky (40-80 machines see 50% packet loss)
- ~8 network maintenances (4 might cause ~30-minute random connectivity losses)
- ~12 router reloads (takes out DNS and external vips for a couple minutes)
- ~3 router failures (have to immediately pull traffic for an hour)
- ~dozens of minor 30-second blips for dns
- ~1000 individual machine failures
- ~thousands of hard drive failures
in addition to "
slow disks, bad memory, misconfigured machines, flaky machines, etc.".
