Free Snapshots?

Peter Baer Galvin

Over the past few months, I’ve been covering new and useful Solaris 8 features in the Solaris Companion. This month continues the trend by looking at the new fssnap command, which provides snapshot copies of the default UFS file system, much like commercial file systems provide. But is it a winner like UFS logging and IP multipathing? This month I test fssnap, I provide useful new reference services, and some feedback on a previous column.

Much Ado About Nothing

What a contrast there is between Sun and Microsoft. I recently attended the Windows XP launch to see what the fuss was about. The three-hour seminar by Microsoft employees conveyed these important XP points:

• All previous operating systems by Microsoft had serious flaws, including inefficient user interfaces and a lack of reliability.

• Look how cool our new screen savers are.

• Look at these games we include!

I thought about what the industry would do if Sun had a press conference about a new release of Solaris and said similar things about their operating system. In fact, Sun tends to do the opposite of Microsoft publicity — they have great engineers who busily add lots of interesting features to Solaris, and then they leave it up to the end users to find them, figure out how they work, and figure out how to use them!

Snapshots, in Theory

On that note, my column this month explores another hidden Solaris feature — UFS snapshots. A snapshot can be thought of as a cousin of RAID 1. Rather than performing a block-by-block copy of a disk, and then performing all writes to both copies, a snapshot takes a shortcut. The snapshot starts from an original disk (in this case, actually a UFS partition) and instead of copying all of the original blocks, it creates a copy of the metadata structures. In essence, it has pointers to all the data blocks.