In the room
Two candidates can draw the same boxes and get different levels. The difference is what each one says before being asked: the number, the price of the choice, the failure that matters. Here are twenty sentences that say it, and when each one belongs.
What does "seniority" sound like in a system design interview?
It sounds like answers that arrive before the questions. A senior candidate puts a number on a choice before making it, says what the choice costs in the same breath, and names the failure that worries them without being asked. The diagram can be identical to a mid-level one. What differs is how much of the interviewer’s rubric gets covered without prompting.
Should I memorise phrases for the interview?
Memorise the shapes, not the words. A phrase like "that buys A at the cost of B" only works when you can fill in A and B for the design on the board, with a number where there is one. A rehearsed phrase with nothing behind it is easy to spot, and the follow-up question exposes it at once. Practise each sentence on two or three different prompts until the shape comes out on its own.
How do I end a system design interview?
With a close of about thirty seconds, even if the interviewer has not asked for one. Say the requirements you designed to, the approach you committed to and its one reason, the trade-off you accepted, and the one decision you would revisit at ten times the scale. The last part matters most, because it shows you know where the design stops working.
Is it all right to say I do not know a technology?
Yes, in one sentence, and then reason from the mechanism the technology must use. Most systems an interviewer names are a replicated log, a partitioned store, or a consensus group underneath. Ask which property the design needs from it, such as ordering or durability, and answer in terms of that property. Bluffing the internals loses more than admitting the gap.
How much should I talk during the round?
Enough that the interviewer never has to guess what you are doing or why. Narrate the phase you are in, say each assumption as an assumption, and say each trade-off as one sentence. Said at an unhurried pace, all twenty sentences in the phrase bank take a few minutes together, so talking through your reasoning costs little of the hour.