We've been using mysqldump to do daily full database backups in case our hardware on our DB server fails. This causes some problems because for a short period of 4 minutes or so, the site in inaccessible because mysqldump has the db locked.
I do a full mysqldump of 100+ wikis and 25+ blogs. It takes and average of 55 seconds to dump and gzip. It auto-runs at around midnight Eastern time. Never a problem. Saved to a RAID 1 device daily and all backups are copied to an offsite RAID 5 device weekly.
How big is your resulting dump... and how powerful is the dumper? 4 minutes sounds excessive. Gzipped, my backups are 156meg. Unzipped, 1.2 gig. Around the time of the backup, I have between 17 and 21 meg of bandwidth hitting the site: around 2600 hits, just under 1000 page views. If I adjusted my backup time to 6am Eastern - that's when I have the least traffic - 2meg of bandwidth usage.
- MHart