HP SmartArray P410 RAID Controller - Rebuild when reconnecting HDD?

[yveZ]

Dear friends,

I have a HP SmartArray 410i card with battery backup and 1GB of BBWC cache. I have 5 disks connected in a RAID5 array. This is installed in a custom built NAS running the latest Windows 10 and using the HPE Smart Storage Administration tool.
I have a dodgy disk noise that I wanted to troubleshoot. My idea was to disconnect 1 drive at a time to see if the noise goes away so i know for sure which is the bad disk. Now, i had disconnected Disk 1 for roughly 15 seconds and then reconnected it. Obviously I got a warning message...but was surprised me is that HPE SSA tool also said "Logical drive 1 is rebuilding fault tolerance data".
Obviously I then stopped the troubleshooting, because I am unclear if is actually rebuilding the data or not.

In short my question comes down to this: When you disconnect a disk from a RAID5 array but reconnect it, why is it then rebuilding the data on it? It is already there no?

If it is not actually rebuilding the entire array, does that mean I can resume the process -during the rebuild message- and go to disk2 to disconnect?

I hope someone can help me, but either way, thank you!
Yves

[Ihaqueit]

In short my question comes down to this: When you disconnect a disk from a RAID5 array but reconnect it, why is it then rebuilding the data on it? It is already there no?

First, RAID 5 need 3 disks, you assigned all disk as RAID5, not assigned one disk as a spare.

Second, RAID 5 also uses parity to check data for accuracy, in your case how you know which disk dont have any data.

If you remove or disconnect after connect it should be rebuild and wait to complete.

If it is not actually rebuilding the entire array, does that mean I can resume the process -during the rebuild message- and go to disk2 to disconnect?

Not an issue, at a time only disconnect or remove one drive to check.

[AmRa · Accepted solution]

When you disconnect a disk that’s part of a RAID disk set and then reconnect it, the disk needs to be repaired so that it contains the latest data.

The disk is repaired automatically (rebuild) whenever you disconnect and reconnect it. If you want to remove another drive from same array then wait until rebuild is completed.

[yveZ]

Not sure what made you think I needed a RAID lesson, but thank you.. You are wrong, during parity initialisation, if you disconnect another disk, it breaks the array. I know because I just tried. But thanks for the try!

[yveZ]

So that explains the parity...that makes 100% sense and I did not know that, so thank you. Also yes, during parity initialisation, if you disconnect another disk it breaks the array. Thankfully I could re-initialise, but now I know for sure!