Before buying a new cache drive is this how a cache pool works?

[xxredxpandaxx]

From what I understand the cache pool works my adding up the total space of the drives and divides it by 2 for a *RAID 1*? I currently have a 256gb cache drive and I was thinking about getting a 1tb drive to replace it. If I were to just add it would I get 628gb of space?  Also if the 1tb failed I would loose data but if the 256 failed I would still have everything?

[JorgeB]

http://carfax.org.uk/btrfs-usage/

[xxredxpandaxx]

http://carfax.org.uk/btrfs-usage/

 

I have already seen this link, I am asking if this is how it works or not.

[JorgeB]

If you saw the link then you should be able to see that's not how it works: 250 + 1TB = 250GB usable space

[morti]

The only way to use all of the capacity is without parity/security

[trurl]

If you saw the link then you should be able to see that's not how it works: 250 + 1TB = 250GB usable space

This is because it must make sure that all data has another copy on another device. So if one of the devices is smaller, it cannot do any more than the smaller disk. It gets a little more complicated if you have more than 2 devices, but it's still making sure there is another copy of everything on another disk. The calculator linked works for those situations too.

 

It wouldn't fulfill the R (redundant) in RAID if it didn't do this.

[xxredxpandaxx]

If you saw the link then you should be able to see that's not how it works: 250 + 1TB = 250GB usable space

 

This is a much better response than just posting a link.

 

Seeing as it works like a regular RAID 1 than how do more than 2 disks work? for example in this.

Does the 1tb act as a back up for each 500gb drive?

 

[John_M]

It doesn't work like regular RAID 1, though. With three disks RAID 1 would maintain three copies of your files. BTRFS RAID 1 maintains two copies that are guaranteed to be on different disks. In your example the two 500 GB disks each mirror half of the 1 TB disk.