What happens if disk shelf loses power but server doesn't?

[GrantE]

I have my unraid server attached to a separate disk shelf for more storage (because they just don't build big cheap cases like they used to).  Not a real commercial disk shelf, just an old case with a PSU, SAS expander card and drives in it, connected via external SFF-8088 cables to a HBA in the server.

 

Right now both the server and disk shelf are on the same UPS, so if they lose power and the UPS dies, at least they die at the same time and it's no different than if they were all in the same machine.  But I'm thinking I may need to split them up across 2 UPSes. Which means that one UPS might fail before the other.

 

Even if I don't use 2 UPSes, this could come up if the power supply in the disk shelf dies.

 

What is likely to happen if unraid suddenly loses access to half its disks while the array is running?

[trurl]

Any disk that can't be written will be disabled because it is out-of-sync. You can have as many disabled disks as you have parity disks and still recover any missed writes by rebuilding.

[ChatNoir]

38 minutes ago, GrantE said:

Right now both the server and disk shelf are on the same UPS, so if they lose power and the UPS dies, at least they die at the same time and it's no different than if they were all in the same machine.  But I'm thinking I may need to split them up across 2 UPSes. Which means that one UPS might fail before the other.

An UPS is not really supposed to die on you when the power is lost. It is suppose to shut down the server cleanly so you do not loose data.

If you set it up this way, you should be OK.

Also, a drained battery is rarely in great shape afterwards and it will take quite some time to fill back up, especially with a parity check/build running on the server after the unclean shutdown.

[Frank1940]

You should really initiate a automatic shutdown of your server about 30 seconds after the normal time that the power might be out if the power outage/disruption might last if it was caused by the Power Provider doing a normal load switching function.  (In my case that is 10 seconds after the interruption first occurs!  IF it last longer than thirty seconds, it will be out for hours!!!)  

 

For the longest UPS battery  life, @ChatNoir is correct.  Shutdown quickly so you can repeat the process a second time if you restart the server too soon...)