Comment 4 for bug 952727

This is actually something that got lost in translation from the old tool to the new one. I believe if you look at the old tool you'll see that by default, it does group-by-disk, but only over the last interval of time as it continues to sample new snapshots and print them out. If you changed the mode or something, it would indeed reach back to sample 0 and print out a line representing the differences from $start to $now, but then as it began iterating forward again, it would be $now1 - $now, $now2 - $now1, and so on.

When the tool is working on a static file, on the other hand, group-by-disk always groups the whole thing, from sample 0 to sample N, into one line per disk.

So this is a case where we need a special behavior. It's difficult to explain, specify, and document, but it's the behavior people will expect by default. It's also subtle, which is why it wasn't noticed right away.

If we change the default group-by to "all," will that solve the problem immediately?