Eh. Google will get out the tapes, retrieve the last backup, merge it with the current, and that's it.
rumborak
Tapes, really?
Yeah, both my current and my last company (both 100% software companies) used tapes for backups. The thing is, there is no better medium for bulk backup really. You can store 1.5TB on top-end tapes in one swoop, whereas Blu-Ray has 50GB max.
And keeping a copy live on a second set of hard disks would be very expensive.
rumborak
If the company has the cash, virtual tape libraries are where it's at. We have a pair of EMC DD880s that do full deduplication of data, compression, and realtime replication to a backup unit in another datacenter across the country. Raw space is about 50TB per node, but it's expandable into the PB range. We've been slowly migrating things off LTO4 tape for the last 8 months or so and have had fantastic results. I've gone from being able to do point-in time restore windows of 3 weeks on my database clusters to 2 months and have been able to run full backups every night (instead of once per week). The coolest thing about the dedupe appliances is that it scans everything at the bit level and only actually stores the "new" bits of data.
My guess is that this sort of thing what Google is probably using for their backups - with tapes only used for long-term archives.