== Using fully mirrored system disks on Linux

I'm [[on record WorkstationPartitioning]] as building systems that use
mirrored system disks with plain _/boot_ and swap partitions (that is,
non mirrored, just duplicated), mostly through ancient caution.

You know what? I was wrong. Totally wrong. I've now built a system with
a fully mirrored system disk and not only does it work, it works better
than my old way. I will henceforth now mirror _/boot_ and swap, in
addition to all of the regular filesystems, on all future systems that I
build with mirrored system disks.

With _/boot_, mirroring keeps things in sync automatically, and it
means that the system will come up without manual intervention when
there's only one disk. With a _/boot_ and a _/boot2_, not only do
you have to keep them in sync by hand (in practice we don't), but
if a disk fails the system will pause in boot because one of your
filesystems isn't there and you have to fix it by hand.

With swap, [[you probably don't need that much swap
../sysadmin/SwapSizingII]], it works, and while init scripts seem to
be much more tolerant of missing swap areas than missing filesystems I
don't see any reason to take chances if I don't have to. And 'mirror
everything' is a very simple rule to keep straight.

(I don't have any idea of the performance tradeoffs of mirrored swap
versus non-mirrored swap, but my view these days is that if you are
worried about the performance characteristics of your swap space,
something horrible has gone wrong to start with.)