unRaid stability after power outage/crash

[Dr_Cox1911]

Greetings,

 

me again, but this time with a question regarding the stability of the unRaid array after a power outage or crash?

Currently I don't have a UPS and at the beginning no parity drive. With my current setup (Debian + Ext4 drives) it survived a couple of power outages really well with absolutely no data loss/repairing.

 

I know that you can't garantee me anything, but a few user reports would be nice.

Thanks guys!

[Squid]

unRaid is no different than any other OS made in history.  If the power failure should happen during writes to a hard drive, then by definition that write is incomplete, and there may (or may not) wind up being some corruption.

 

That being said, XFS seems to be really good at not corrupting itself.  BTRFS (if you use a cache pool) seems to want to get corrupted in this case.

 

Either way, IMHO a UPS is required on any computer system that contains data you actually care about.

[tdallen]

If your server shuts down due to power loss, unRAID will consider it an unclean shutdown and start a parity check when the server comes back up.  As Squid points out data loss is possible but unlikely unless you are writing to your server.  That said, the parity check is inconvenient and time consuming.  I live in an area with a decent number of short power interruptions, combined with occasional long ones.  I have a UPS to deal with the short interruptions.

[Dr_Cox1911]

On 24.10.2017 at 11:38 PM, Squid said:

unRaid is no different than any other OS made in history.

So the extra features introduced by unRaid like usershares, parity, cache, ... don't really matter, because it's still basically XFS that has to take the beating after a outage.

 

On 25.10.2017 at 4:49 PM, tdallen said:

If your server shuts down due to power loss, unRAID will consider it an unclean shutdown and start a parity check when the server comes back up.

What will unRaid do if I have no parity disk?

 

And thanks for the answers, Squid and tdallen

[tdallen]

2 hours ago, Dr_Cox1911 said:

What will unRaid do if I have no parity disk?

I've always run with parity so I'm not sure what steps unRAID will automatically take when recovering from an unclean shutdown (other than the parity check).  It should be less time consuming, at any rate.  Hopefully someone who has more direct knowledge will chime in.

[JorgeB]

I've always run with parity so I'm not sure what steps unRAID will automatically take when recovering from an unclean shutdown (other than the parity check).  It should be less time consuming, at any rate.  Hopefully someone who has more direct knowledge will chime in.

 

Without parity there's nothing to check, array will star normally, there's a small chance one ore more disks will come up unmountable, but it's the same with parity in that regard.

 

 

[Delarius]

I just had my first unexpected power outage with UnRAID.

When power came on, parity check started. 

Parity check ended . 18 errors.

Tested everything and it seems fine. While undesirable, power outages don't typically corrupt data. The caveat being if there's heavy writing to disk when power off occurs - bad things can happen. 

Fortunately, it's generally obvious if you're doing heavy writes at the time of shutdown. I think I was using Plex docker and testing ownCloud docker.

 

Last check completed on Tue 14 Nov 2017 07:55:59 AM PST (today), finding 18 errors. 
Duration: 13 hours, 38 minutes, 34 seconds. Average speed: 81.5 MB/sec

 

Just a comment but some evidence to suggest that while a UPS is a very good addition to UnRAID, it's not required. 

Neither is house insurance. 

Backups, backups, backups. If you have one, you have none. If you have two, you might have one.

[bonienl]

7 hours ago, Delarius said:

Parity check ended . 18 errors.

 

These are parity sync errors. Due to the power outage parity wasn't fully updated and got out of sync. You need to run a correcting parity check.

 

[Delarius]

4 hours ago, bonienl said:

 

These are parity sync errors. Due to the power outage parity wasn't fully updated and got out of sync. You need to run a correcting parity check.

 

I'm not sure I understand.  I was simply explaining what happened when I experienced a power outage and automatically ran a correcting parity check. I don't believe running another correcting parity check would be useful.