What happens when you unplug 1 or more devices from an mdadm RAID array to simulate a failure in Linux Ubuntu/Centos/Debian?
In short the two drives in the array were /dev/sdd and /dev/sde. The kernel sees they were unplugged and have gone down as you can see below.
mdadm caught the first one being unplugged /dev/sde and disabled the missing drive. However when the final drive that was part of the array is unplugged it didn't notice at all. Instead it complains about an IO error later for drives that the kernel knows do not exist anymore.
[45817.162728] ata4: exception........
What a hdd hard drive and mdadm RAID array failure looks like in Linux
[3805108.257042] sd 0:0:0:0: [sda] 1953525168 512-byte hardware sectors: (1.00 TB/931 GiB)
[3805108.257052] sd 0:0:0:0: [sda] Write Protect is off
[3805108.257054] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[3805108.257066] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[3805108.257083] sd 0:0:0:0: [sda] 1953525168 512-byte hardware sectors: (1.00 TB/931 GiB)
[3805108.257090] sd 0:0:0:0: [sda] Write Protect is off........
Powersupply Issue, Motherboard AHCI issue?
This is the most I can get when plugging in a hard drive hot and only on some power connectors.
[71656.314271] ata5: exception Emask 0x50 SAct 0x0 SErr 0x90a02 action 0xe frozen
[71656.314277] ata5: irq_stat 0x00400000, PHY RDY changed
[71656.314285] ata5: SError: { RecovComm Persist HostInt PHYRdyChg 10B8B }
[71656.314294] ata5: hard resetting link
[71660.360686] ata5: softreset failed (device not ready)
[71660.360694] ata5: applying........
mdadm RAID 1 adventures
I separated the 2 drives in the RAID 1 array.
1 is the old one /dev/sda and is out of date, while the separated other one /dev/sdc was in another drive and mounted and used with more data (updated).
I wonder how mdadm will handle this:
usb-storage: device scan complete
md: md127 stopped.
md: bind
md: md127: raid array is not clean -- starting background reconstruction
raid1: raid set md127 active with 1 out of 2 m........
Linux AHCI Hotswap Tips - Remember To Reread The Partition Table WITHOUT rebooting
From the package "parted" you can use the command "partprobe" to re-read the partition table. I really hate rebooting, and that's what Iloved to hear about AHCI motherboards, that they allow hotswap so you don't have to reboot. But that's only as good as the OS, if the OS does not reload the partition table you won't be able to do anything with that new drive you attached without rebooting. Yes, even without re-reading the partiton table Linux will........