One of the main reasons why I purchased a Drobo S was because it implemented a scrubbing feature (usually called a consistency check) on a regular basis, which should be able to find & correct bad spots that develop before they cause problems. I schedule such checks monthly for RAIDs at work.
However, I have never seen nor heard any indication that any scrubbing is happening on my Drobo S. No blinking of lights, nothing in Dashboard to tell me that it has happened, nor is there any method to manually kick off a scrub. It seems to me that if scrubs were happening when there isn’t any activity that I would be seeing the drive lights flicker and one or more drives sound active, but I’ve not seen/heard anything like that (though I guess it would be very quiet if the scrubs go sequentially through the drives rather than across the stripes). I have Dashboard set for Drobo to send alert “on all useful information”, but I’ve never noticed a pop-up or anything in the Windows Event Logs about scrubbing.
If I am going to change out a drive for a larger drive it would be EXTREMELY good to know that all the data areas on the remaining drives are good before removing a drive. If you remove a drive and one of the other drives has a bad spot, the file that is in that bad area is hosed. But almost certainly you could have read the file if the old drive had been in place. A scrub/consistency check is therefore a very prudent thing to do before removing any drive.
So here are my questions/comments:
How can we know that scrubbing really is taking place?
When the drives go to sleep, or the Drobo S is shut down, does it restart scrubbing from the beginning, or does it pick up from where it last left off?
I understand that all scrubbing should stop when there is disk activity in order to not slow down access, but how quickly after the activity is through does scrubbing resume?
Is data parity verified during a scrub, or are physical defects the only thing that is checked for?
Since there currently doesn’t seem to be any way to know when a scrub cycle has been completed, can you at least let us know some sort of guideline as to how long it takes to do a complete scrub? e.g. “a scrub is accomplished at a rate of approximately 2TB/hour, so if you have 6TB the Drobo needs to be inactive (and drives not spun down) for 3 hours for a complete scrub to take place” This would help us in setting our drive sleep settings.
Since my drives never go to sleep (which I’ll contact Customer Care about), does that mean that scrubs have been taking place continually for months?
Feature request: I really want to be able to kick off a complete scrub at the time of my choosing, and know when it is complete, both for peace of mind, as well as to know things are OK before swapping out a drive. This manual scrub should over-ride any drive spin-down settings until after the scrub is complete, and continue regardless of user disk access. I’m going to put this into the “Feature Request” section as well.