RAID with three disks (RAID 5 vs RAID 1E)

I am upgrading a server which has four drive bays. I'll be putting a new Adaptec RAID card into the server so it will support large drive sizes. I need to squeeze as much capacity as possible out of this four-drive cage, so 8 TB drives are my most likely choice.

This is a generic file server (but it handles recording video streams from a security system). I would like to use one of the drive bays for a hot standby, which leaves me with three disks to form the RAID array.

Although I could simply use two disks for mirroring + one hot spare, I've seen RAID 1E (spread over three disks + one hot spare, or RAID 5 three disks + one spare.

Is there a good reason to go one way or the other?

I read the question R5 vs R1E, but it doesn't really answer if R5 or R1E is better in the case of a good controller and multiple write streams.

Solution 1:

You should carefully consider whether RAID 5 will work for you especially in a RAID rebuild situation. The amount of reads required to rebuild a RAID 5 array is significant and can fall foul of an Unrecoverable Read Error (URE) which will cause you to loose the array and have to recover the data from backups. For example typical 8TB drives have 1 URE per 10^14 bits read so for your array there is a significant chance (~85%*) that you will not complete the rebuild.

Do you and your data a favor, use RAID 10 and a hot swapable disk system. Keep a spare disk to hand.

^*Yes that's a fairly naive view and you may get lucky but ... Did he fire six shots or only five?

Solution 2:

The answer hasn't been RAID 5 for at least a decade, it's as dead as punch-tape - use 4 disks and RAID 10 it.