I'm very new to Unraid and have a trial running on a test system.  Previously while testing with some old drives, I live-swapped some SATA cables around on drives as I was adding an SSD for a cache drive and found it odd that the Unraid web interface didn't freak out or show drives offline, even refreshing the "Main" tab.  It was some time later (30ish minutes to a couple hours), all these notifications rolled in about parity errors, read errors, etc.  Not sure why I didn't post/ask about it then.

 

Today I swapped in my production drives to get my array up and going for good (purchase pending once my new USB drive is delivered) and again, did it while the system was running.  I didn't have the luxury of time to wait for it to start erroring, but sure enough, it made it look like everything was fine.  I had to stop/start the array to get it to realize the drives weren't there.

 

I realize what I was doing is far from the norm, but it does beg the question of how "real time" alerting of future disk failure or error reporting will be, and whether the delay will affect proper parity calculation.  Is this normal?  I wasn't USING the array other than an unconfigured but running mariadb docker) so with no writes/reads maybe it had not had the opportunity to realize the disks were gone (seems unlikely as the OS should have seen the device removal)?

 

Appreciate any input you may have.  Thanks!

For array devices you'll only get a notification when Unraid tries to read or write to the disk and it can't. 

Rather than just to a particular disk, I would assume this would be for any write to the array (which necessitates a parity calculation and hence a read from all disks), correct?

AFAIK, a write does not automatically require to read all drives, it depends if turbo write is enabled or not.

The default behavior is to read the content of the block on the drive, change it and update parity.

 

In that case, if disk 1 dropped and you only access disk 2, it might not be detected immediately.

2 hours ago, HawkZ said:

Rather than just to a particular disk, I would assume this would be for any write to the array (which necessitates a parity calculation and hence a read from all disks), correct?

You might find this section of the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page to be off help in understanding Unraid write modes.

11 hours ago, itimpi said:

You might find this section of the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page to be off help in understanding Unraid write modes.

Great read and explains this very well.  In this case the drive with issues was my parity drive so would have been touched at any write (which I really wasn't doing unless the system was doing anything in the background).  Thank you!

There is no good reason to "hotswap" array or pool disks since Unraid will not do anything with a new disk until you assign it, and you can't change disk assignments without stopping the array.

 

Also, when a disk disconnects (or is disconnected) and then reconnects (or is reconnected) it will reconnect as a different device (sdX  designation) since the previous device was already in use. When this happens, the expected connection isn't there anymore and so the disk is missing.