Update to section 19.4 on disk mirroring

[John R Levine]

>> setting up bootable gmirror disks isn't wrong, it's seriously suboptimal since
>> it involves a needless full copy of a disk, which takes hours rather than five
>> minutes if you do it the easy way.
>
> In my case I found it to be an almost perfect procedure, because it
> doesn't require bootable CD media. The disk copy in occurs while
> the system is multiuser, and if you ignore the instruction to drop to
> single user to start the resync, it'll still take Not That Long.

It doesn't strike me as a good idea to do the first disk copy as multiuser 
unless you don't care about losing files that change during the copy.  I 
agree that you can do the insert and resync in multiuser.

> I don't suppose many people are in the position of not being able to boot
> a fixit CD though.

They're pretty easy to download and burn, and if you care enough about 
your system to do disk mirrors, I expect you'll probably keep a set of CDs 
around in case of non-hardware disasters.

Regards,
John Levine, johnl at taugh.com, Taughannock Networks, Trumansburg NY
"I dropped the toothpaste", said Tom, crestfallenly.