Raid 5+1 considerations

Question

I am charged with upgrading a persons private business network and was thinking of putting a bit of backup and centralisation. So for that i though of getting a small NAS with 4 drives and having 3 drives in RAID 5 (for backup and availability in case of disk death) and 1 drive in RAID 1 with the RAID 5 disks (for performance).

As this is a small business (3 people working), the budget is not great (why the 4 disk NAS).

I would like to know your considerations/thoughts about this setup, is it reliable ? Is it usefull ? Is it even doable ? In the event of a disk failure in the RAID 5 array, what would be the diffculty of reconstructing the array ? I am not new to the IT world but am quite the novice when it comes to BUP and storage availability. I was also thinking about having one disk as the active workspace and then the RAID 5 as a backup that would occur every night or so. I'm hesetating between both.

Here is an illustration of my idea : NAS Raid setup idea

Be fair with your answers please :). Thanks in advance.

Answer 1

If you are using large (say >1TB) consumer drives, RAID5 is probably not your safest bet. In no situation is your weird RAID 1 of (Single drive)+(3 drive RAID5) a good layout at all.

The reason behind that is that the larger the drives, the more likely you'll encounter some sort of read error. This can often go undetected for a long time, if nothing actually tries to read that particular block. When a drive fails however, and you put in a new disk to recover the missing information, it has to read every single block on the remaining drives. If any one of them has an issue, your rebuild will fail. Some RAID systems can handle this somewhat gracefully, and you'll lose whatever data was stored in those blocks. Others just give up and you lose everything. For a low budget 4 disk NAS, expect the "give up and lose everything" behaviour.

Doing your weird RAID 1 of (Single drive)+(3 drive RAID5) set will not give you any benefits. For starters, you'll be limited to the capacity of the single drive. So you'd have a FAR safer system by doing RAID 1 across 4 disks. Or RAID 10. You'll also run into weird problems because some disks get used more heavily than others, making access slower.

In addition, RAID is not a backup solution. RAID is there to give you availability. Backups cover a lot more than a single drive failing - they are your plan for when any of the following happen:

• Someone accidentally deletes an important file, or it gets corrupted
• Someone opens a virus email, gets Cryptolocker, which promptly encrypts everything on your network drives.
• A single hard drive fails.
• Multiple hard drives fail simultaneously.
• A power surge or other fault destroys your NAS.
• Your building burns down/floods/gets taken over by hostile aliens.

RAID saves you from one of those, but does nothing to help with the rest. RAID allows you to keep good uptime because the service isn't down while you swap out a bad drive.