Pioneer changed its machines radically beginning with the 640, so it has the same operating system as the followup 550 and 560 (only difference is the 640 was the last to use EIDE hard drives, the later models are SATA).
Unfortunately there just isn't any official info to fully explain how the "Optimize" feature of the 640-550-560 works, or to suggest when/how to use it. I can only give you my opinion based on personal use, which I posted earlier: optimizing isn't particularly necessary and can be dangerous if activated on a drive with corrupt sectors.
A "healthy" Pioneer HDD thats 60%-70% full should take about 90 to 160 mins to finish optimizing. If you are seeing completion times of 8 hours, you should probably avoid using the feature: either the aging HDD has too many errors to optimize efficiently, or the HDD is too full and doesn't have enough free space to permit effective optimization.
What is your usage pattern? Optimization might
improve performance and reliability if your HDD is full of a great many short clips, or over 100 TV shows with the commercials edited out. But if you mostly use the HDD to timeshift (record>watch>erase) and don't leave edited videos on it long-term, there's nothing to be gained from optimizing.
I never optimize my own 540 and 640: they're too old, the risk of video loss during the process is not worth the (mostly theoretical) benefits. Pioneer has indicated its later models like the 640 automatically perform casual optimization as long as there is free space on the HDD, mostly this involves "collapsing" recently edited titles to avoid too many fragments. I suspect this might be what the scary "Repairing HDD" alert really means.
Originally Posted by Kelson
Bear, I'm not sure that actually applies to a HDD. The heads fly over the platter on an air cushion and never make contact with the surface to give it any wear. The magnetization curve and coercivity of the magnetic materials does not change from repeated read/writes. Perhaps you are thinking of something mechanical?
You're right, of course: I tend to think of it as "wear" but the true reasoning (suggested by Pioneer) is to spread the risk of a sector going bad by not repeatedly gambling on the same area of the HDD. If you alternate heavy use of different portions of the media, you reduce the risk of potential glitches. Pioneers will sometimes fail to HS copy a recording from HDD to DVD if the recording has a bad sector: you can load DVD after DVD and each will fail with a "Cannot Complete Copy" alert. Besides being inconvenient, this wastes a lot of DVDs until you realize what the issue is. I find it happens less now that I alternate my HDD usage areas. YMMV, in the long run neither optimizing nor my "system" amounts to much. Avoiding too many fragmented titles is helpful if the HDD is nearly full, the Catch-22 being a full disk is more difficult and dangerous to optimize.