Courtesy of a recent entry , I wasreading over my dotfiles when I stumbled over a remnant of a ratherpeculiar and annoying Unix (unfortunately, I no longer remember whichone it was). This Unix was notable for a simple reason: it didn't havea test program.

You might sensibly ask how on earth anything that can possibly callitself a Unix would be missing such a basic thing; after all, without test a lot of scripts don't work at all, since test is also known

Given the downsides covered in yesterday's entry , ZFS's decision to stripe data blocks acrossall of the disks in a raidz probably sounds rather odd. However, itactually is a sensible decision given ZFS's overall design goals. Theeasiest way to see why is to contemplate the problems posed by analternate design.

Suppose that ZFS did not turn a single data block into a 'paritystripe', but instead had the idea of what I will call a 'block set',a group of