In my previous post I forgot to mention the other big win of having My Documents redirected to a share on a Windows 2003 server - shadow copies. In technical terms this is a periodic volume snapshot service, using copy-on-write to minimize disk space requirements. In user terms it means that you can recover from most common filesystem goofs - erasing yesterday's document, overwriting last week's spreadsheet - without even needing to 'fess up to your helpdesk. Just browse back through the snapshots of My Documents and find the last good copy of your file. It's like a little time machine for bits.

Needless to say, system administrators are also keen on shadow copies - for them it means less mounting of backup tapes, less juggling of restore jobs, just walking the user through the process over the phone. For more on the administrative side of shadow copies, see Adi Oltean's weblog.

Note that copy-on-write snapshots have been around for a while, but this is a particularly nice implementation. When I used AFS as a filesystem, it always kept “yesterday's” snapshot around, but woe betide you if the goof was more than a day ago. As set up at Microsoft, Windows Server 2003 defaults to two snapshots per day (except for weekends - go figure!), and keeps them accessible for two weeks.

Of course, AFS was also a distributed filesystem, and as such suffered from the same fundamental problem as most early distributed systems:

“A distributed system is one in which the failure of a computer you didn't even know existed can render your own computer unusable” - Leslie Lamport

I'm very glad that those days are behind me��