(I've posted this on Serverfault as I suspect it a bit to technical for Superuser. If I'm wrong please move it where appropriate)
I am remotely looking at a device which identifies as ReadyNAS ProUltra2 V1.4. It appears this device has 2 disks in it and runs a variant of Debian. I have noticed something concerning about the RAID array - It reports as follows
ReadyNAS:~# cat /proc/mdstat Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] md2 : active raid5 sda3 sdb3 972040704 blocks super 1.2 level 5, 64k chunk, algorithm 2 [2/2] [UU] md1 : active raid1 sda2 sdb2 524276 blocks super 1.2 [2/2] [UU] md0 : active raid1 sda1 sdb1 4193268 blocks super 1.2 [2/2] [UU]
Of concern is that md2 (which appears to be most of the space) is configured as RAID5 but with only 2 disks. From doing some reading I understood that mdadm requires a minimum of 3 disks for redundancy in a RAID5 configuration. I have no idea if this understanding is wrong, if the ReadyNAS is doing something non-standard or if this was incorrectly set up by whoever set it up - although I don't know why RAID5 would be enabled on a box like this one appears to be, and the person who set it up must have used a gui based setup process of some sort as they are not technical.
Anyone know if MD2 actually has redundancy or how this setup may have come into being ?