Retrospect 10 and Instant Scan
A year after returning to private ownership after suffering under a series of uninterested corporate owners, Retrospect Inc. has simultaneously released Retrospect 10 for Mac and Retrospect 8 for Windows.
Instant Scan runs as a background process on Retrospect servers and clients to maintain a list of all the files and folders present on HFS+ (Mac) and NTFS (Windows) volumes. It uses FSEvents on OS X and the USN change journal on Windows to keep track of new, changed, moved, and deleted files. When it’s time for a backup or a restore, Retrospect gets the file listing from Instant Scan, instead of needing to scan each volume, as it did in previous versions.
Synk’s Live Sync (formerly ZeroScan) and Time Machine also use FSEvents. I’m not very fond of this approach, as it introduces an additional point of failure. Indeed, one of the FAQs is about how to rebuild the scan file if you think it’s corrupted; another is about how a file added 30 minutes ago might not be included in the current backup.
Instant Scan lets the Retrospect server back up more clients in a specified amount of time. However, to me it seems that the bottleneck is not the slow client scanning but the fact that the server only backs up one client at once. (At least, that’s how it worked the last time I used the product.) My guess is that backup throughput would be much higher if the server could let multiple clients do their slow scans simultaneously rather than have clients “instant” scan one-by-one.
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Also, I don't know how SuperDuper does it, but it is fast without relying on FSEvents. I wish SuperDuper would make another product for incremental backups as well.
How about Arq, actually? Does it rely on FSEvents?
@charles I think SuperDuper uses fts. I also use it in DropDMG and found it much faster than the alternatives. Arq does a full scan without relying on FSEvents.
