GEOM, Vinum difference

[Michel Talon]

Rakhesh Sasidharan wrote:

> Another (related) question: both gvinum and the geom utilities like 
> gmirror and gstripe etc provide for RAID0, RAID1, and RAID3. Any 
> advantages/ disadvantages of using one instead of the other?

There has been a polemic between Greg Lehey and PJ Dawidek about the
comparative advantages of raid3 and raid5. You can find the exchanges on
Google. One example being:
http://arkiv.freebsd.se/?ml=freebsd-performance&a=2004-08&t=227183
As far as i remember there are arguments showing that raid3 is better
than raid5 both in terms of speed and of data security. It seems that
raid5 has mostly a hype factor for him, but i may err. Anyways it is for
such reasons that in the modern geom system, raid3 has been implemented
and not raid5. But vinum has been ported to the geom framework for the
benefit of old users, or of people who like it. For example if you are
using FreeBSD-4 or DragonFlyBSD, vinum is the standard tool, and you
may prefer getting expertise in just one tool.

Finally none of these raid systems is really good, both for performance
and security. If you are concerned with your data and want good write
speed, you must buy enough disks and use raid 10. Another important
factor is ease of use.  The geom tools, gmirror, gstripe, graid3, etc.
are *very* easy to use.  The documentation in the man pages is clear,
sufficient for doing work, and not too long. On the contrary, vinum was
traditionaly documented in a very hermetic way. But more recently, Greg
Lehey has provided a very clear chapter of his book on his web site
which can be recommanded, but is not short. Note the documentation is a
critical aspect of such systems because its lack may bite you in case a
disk crashes and you need to adopt correct procedures under stress.
Also for some time the gvinum stuff was extremely buggy, and was
completely non functional when i tried it. I hope it is fixed now.

-- 

Michel TALON