Windows 7 home backup solution, with offsite provision

Main Volume

I know you said you don't want to build another PC fileserver, but most of the ready-to-go solutions don't have any safeguards against silent data corruption.

If you're looking for data integrity and reliability, you might want to consider running an OpenSolaris fileserver with a raidz2 or raidz3 configuration (2 or 3 parity drives, respectively) on ZFS.

With larger drives, the rebuild time will increase when a drive fails--which also increases the chances of a second-drive failure during the rebuild. But the main advantage of ZFS is that it protects you against silent data corruption, since the filesystem itself is checksummed.

You can also run ZFS on other operating systems, but OpenSolaris is always the most up-do-date version since it takes a while to port new features to the other platforms. If setting up an OpenSolaris box seems a little more work than what you want, FreeNAS seems to be the next best thing, in terms of ZFS support.

On the Linux side, ZFS is not supported in the kernel (only as a user-level driver), but there is also a new filesystem under development, called btrfs. Unfortunately, there is no stable release of btrfs, as of March 2010.

Backup

For your offsite backups, it might be more cost-effective to pay for a service like CrashPlan, Carbonite, or Mozy. It's very, very easy to configure any of these to automatically backup your files. Of the three, CrashPlan has the best backup and recovery features (and even allows you to backup to other remote computers for free), while Mozy's recovery methods are either expensive or very inconvenient (if you want to download a Mozy backup, you have to wait for your job to be queued up and bundled into a zip file). I haven't personally had any experience with Carbonite.

Note that you shouldn't depend solely on an offsite backup--if you backup to the cloud or some other offsite computer, you should also have a local backup.

The Drobo reviews I've seen noted poor write performance, but if you're just using it as a nightly backup drive, it might be sufficient.

Backup rotation

If you want to rotate backups between a local and off-site location, you need at least 3 backups to guarantee one is always local and one is always safe at the off-site location. The third is either in-transit or at one of the other two locations at any given point in time.

ROBOCOPY vs. CrashPlan

ROBOCOPY will cause more wear and tear on your hardware, since it has to read every file during every backup. It's not clear to me whether it only copies changed files or if it copies all files. If ROBOCOPY fails for some reason, it may not be apparent that it has failed, unless you have set something up to reliably report its backup status.

CrashPlan monitors your hard drive for changed files, and only copies the changed files. Since it actively monitors changes to disk, it does not need to read every file in your backup source. CrashPlan automatically e-mails you to notify you how long it has been since the last backup, and how much data was transferred during the last backup.

That said, keep in mind that CrashPlan doesn't have to replace your ROBOCOPY backup scheme. You can use CrashPlan to supplement whichever other backup scheme you happen to choose.

I do not think you can write something that is going to be sufficiently fast enough to keep you happy, while consuming very little CPU and resources. The task of compression into rar, zip, or 7z format is CPU intensive, and disk intensive.

I suspect that a "nearly realtime" system that can almost keep up with your working rates would have to be very intelligent indeed.

If you can not live with an overnight full backup of your Raid0 system, then you shouldn't be using Raid0 at all, in my opinion. I used this exact configuration for my primary system for several years and found no noticeable performance benefit in Raid0 when I did it with a bunch of commodity 7200 rpm drives. Instead, I decided to go with a single Velociraptor drive, and a second drive to back it up to. Lower MTBF risk, and higher performance for the same dollars, and in my opinion, no need for instant realtime backup.

In effect, IF you are trying to turn your Raid0 into something as "safe as Raid5" without losing the benefit of Raid0's speed compared to Raid5. I do not believe it can be done. In fact, I could almost guarantee that Raid5 in-hardware compared to backup-in-software will result in a net loss of usable disk bandwidth that will make your complex system both more likely to fail, and lower performance, than a single Velociraptor drive running unencumbered by realtime backup or RAID.