Extending Storage

[Igotcha]

Hi,

I have a 2 x 3TB WD red mirror raid in my freenas. As I learned, mirror is no real raid, so my questions are:

1. Is it possible to extend my existing setup with additional HDs (more 3TB WD red)? Plug more HDs into it and do some magic configuration?
2. If so, what would be the next step to have real raid data redundancy and perhaps more storage, add at least 1 more 3TB WD red?

I read http://doc.freenas.org/9.10/storage.html#extending-a-zfs-volume but I am not sure what this means:

Code:

to extend a ZFS mirror, add the same number of drives. The resulting striped mirror is a RAID 10. For example, if you have 10 drives, you could start by creating a mirror of two drives, extending this mirror by creating another mirror of two drives, and repeating three more times until all 10 drives have been added.

The first sentence says: Add the same number. So I need to add 2 x 3TB.

The rest reads like: You can extend up to the same initial amount of HDs.

Thanks!

 

[Mirfster]

Are you want to increase your storage space or increase redundancy?

The reason I ask is because you can do either:

• Add another vDev to the Pool; say two more 3TB drives. This will increase the space, but still have the same amount of redundancy (survive one drive failure)
  
• Add another drive to the Mirror and create a 3-Way Mirror. This will increase the redundancy (survive two disk failure) but not the space

You could even make 4-Way Mirror and be able to withstand three drive failures, but not many people are going to go that way using mirrors...

 

[Stux]

As I learned, mirror is no real raid

a mirror is a real raid :-\

 

[danb35]

mirror is no real raid,

What do you mean by this? Because as @Stux said, mirrors are "real RAID", as much as any other RAID configuration. If you want to expand your storage capacity, you can do that most easily by adding pairs of disks in mirrors. Use the Volume Manager to extend your existing pool with the new pair of disks, and repeat as necessary or desired. If you want to increase your redundancy, you can convert your two-disk mirror into a three-disk mirror (though that will unfortunately require using the command line).

Edit: And if you're concerned about the number of disks, add two at a time. You can have any number of disks in your pool, but add two at a time.

 

[Stux]

What do you mean by this? Because as @Stux said, mirrors are "real RAID", as much as any other RAID configuration. If you want to expand your storage capacity, you can do that most easily by adding pairs of disks in mirrors. Use the Volume Manager to extend your existing pool with the new pair of disks, and repeat as necessary or desired. If you want to increase your redundancy, you can convert your two-disk mirror into a three-disk mirror (though that will unfortunately require using the command line).

Edit: And if you're concerned about the number of disks, add two at a time. You can have any number of disks in your pool, but add two at a time.

The only issue with mirrors is if you're concerned about the amount of space (50%) used for redundancy