So, what happens to a relayout when the power goes?

I’d like to find out before the disaster rather than after:

Scenario: I’m doing a lengthy relayout on a Drobo (1st gen for the sake of argument). It’s a long one: the Drobo’s got 8Tb of drives in it, is 2/3 full, so it takes around six days, based on experience. That’s a long time. If there’s a winter storm-generated power failure, what’s likely to happen? Will I likely lose all data? Some data? Relayout starts all over again but no data’s lost? What?

Guesses not appreciated; solid facts please.

We mostly see data loss and data corruption when there is a power outage during relayout.

Relayout is calculation/writing of the fault-tolerance (parity, checksum, whatever) data, so the stored data will be fine.

If the Drobo is in use at the time of the power failure there is the chance of filesystem corruption that will need to be corrected by the connected PC (it’s the same as if you disconnected a regular drive while in use). If the filesystem on the Drobo isn’t journaled (i.e. FAT32), then there’s more likelihood of actual data corruption/loss, but again, this is nothing Drobo-specific.

I have my Drobo and the PC connected to it on a UPS. I have the connected PC shut down shortly after power is lost, so the Drobo then goes to sleep. The UPS won’t last that long (~1 hour), but it’s long enough for Drobo to gracefully sleep.

Will need someone else’s experience for whether relayout restarts from the beginning or has some internal journaling so it can continue from at/near the point it was at when the power was lost.

Thanks for the cogent answers! So, a followup: Assuming no UPS, what’s the best option if a storm comes in? Can a Drobo be safely put into standby during a relayout, then powered off? Or is there another way to safely, manually prepare the Drobo in advance for a loss of power during a relayout?

Or is prayer the only option here?

If you are in the middle of a relayout, and you know the power is going to go out, you can do the following:

Shut down your computer.
Unplug the data cable then the power.
Once the power is restored turn on computer, plug in data cable then power.

Relayout should continue from where it left off.

I would not recommend this procedure but it’s better than letting the power go out when the drobo is connected to your computer.

Agreed, at least if there is no computer connected then the computer wont **** up the file system, you only have to worry about what drobo will or wont do.

however i can say that i have had the power fail on my during a rebuild, the pc wasn’t reading or writing to drobo at he time but it was connected and drobo was rebuilding onto a replacement disk, and when the power came back, drobo just carried on, no obvious corruption or issues.

its still something that you very very much want to try and avoid!

Isn’t the whole point of the battery backup on the Drobo such that you can cut power during a write (or relayout) and it’ll be safe?

that would only be true if drobo wasnt connected to a computer, i suspect, i.e. it protects what drobo is doing to your disks, not what your computer is doing to drobo.

If its a PC writing to a drobo and it has the file system open, then a power loss would cause corruption just the same as with any other USB device

You should have battery backup for both Drobo and the computer, and make sure the computer gracefully shuts down before the battery backup (and hence Drobo) loses power. That’s my configuration.

You recon it makes sense to have a service issuing “drobom shutdown” when the machine is going down or will the fact that the USB port switches off be enough for Drobo to “get the message” and shit down?

If the drobo is rebuilding, it won’t power down even if the attached computet powers down.

I’m not sure you could force it to

However the pc powering down will mean it no longer has the file systrm open, so hppefully drobos internal processes could survive a power outage

As Docchris says, the key is not having the filesystem open or in use, which powering down the PC will do.