Questions about scrubbing

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:

  1. How can we know that scrubbing really is taking place?

  2. 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?

  3. 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?

  4. Is data parity verified during a scrub, or are physical defects the only thing that is checked for?

  5. 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.

  6. 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.



1 Like

why would the drive lights flicker? they tell you the status of the drives - good, needs replacing , or failed. drobo never indicates what the drives are up to.

and no, scrubbing is a totally background process

from my understand it (obviously) only runs when drobo is idle, it wont scrub more than once a month (so if you have enough idle time that it can do it all in 3 days - it does nothing for the next 30ish, and it makes sure it always does a scrub at least ever 3 months

this is from memory from the old forums.

to answeer your questions:

  1. you have to trust DRI that it is

  2. it does it on a continual basis - so it knows what was scrubbed and when and will make sure it checked everything on a semi-regular basis

  3. no idea - but no access is no access, so i would imagine relatively immediately

  4. it think its the full works

  5. i think it gets steadily more aggressive about the prioritising of it if it isnt able to complete/hanst been able to check some sectors for a while, basically dont worry abou tit, an dit will make sure its taking care of things

  6. no - as i said, it wont do it more than once a month, once its done (checked everything it can), its done until next month

Thanks for the information!

I’m surprised that it only does a scrub once a month since that’s contrary to their documentation. According to the Datasheet (which I just checked again to be sure) they claimed: “Even when sitting idle, Drobo S will continually examine the blocks and sectors on every drive…” From how you describe it, they should have said “regularly” instead of “continually”.


well i would imagine that you would run into issues of wear and tear, especially with non-enterprise drives if you were thrashing them 24/7, scrubbing should check for problems, not create them!

plus i dont think disks tend to degrade that quickly, once a month is probably more than adequate

and obviously it wouldn’t be the dictionary definition of continuous because drobo has to do other things too, so would be continually pausing it anyway, soi think its probably good enough, i guess its more meant to imply that your data’s scrub is always “current” i.e. not too old.

I read “continually” in that context to mean “keeps doing it regularly” as opposed to “continuously” in that context, would mean to me that it keeps doing it and is never idle, which would definitely cause unnecessary wear and tear.