Networks use very narrow (in physical size) channels and very limited set of media states to transfer signals
That’s right, and one of the biggest problems we’re facing right now is the storage explosion – we have mountains of cheaply stored data. That’s not a bad thing. But the pipe to get to that data is growing very, very slowly. It’s the disconnect between these two growth rates that’s the problem.
One interesting thing happens as hard drive sizes increase, without any comparable increase in bandwidth to get to the disk: you have to treat them like sequential, tape-style devices.
JG Certainly we have to convert from random disk access to sequential access patterns. Disks will give you 200 accesses per second, so if you read a few kilobytes in each access, you’re in the megabyte-per-second realm, and it will take a year to read a 20-terabyte disk.
If you go to sequential access of larger chunks of the disk, you will get 500 times more bandwidth—you can read or write the disk in a day. So programmers have to start thinking of the disk as a sequential device rather than a random access device.
DP So disks are not random access any more?
JG That’s one of the things that more or less everybody is gravitating toward. The idea of a log-structured file system is much more attractive. There are many other architectural changes that we’ll have to consider in disks with huge capacity and limited bandwidth.