Hello,

I have looked around in the forms and have not found definitive answers to my cache questions.  I am running Unraid 6 on both or my servers and the cache pool is btrfs.

 

1. When looking at the Balance Status both say “No balance found on '/mnt/cache'”, is this normal?  If not what is normal?

 

2. Being that I have 4 drives in the pool (for each server) do I still want to run a Balance with options “-dconvert=raid1 -mconvert=raid1” or should I run something else?

 

3. Is there a process for drive fails for the pool like we do the array?  Meaning do we need to find a drive of the same size or can we replace with a larger drive and NOT LOSE THE DATA. (Sorry for the CAPS but a lot of posts and testing I have done looks like we will lose the data if we do anything with the pool)

 

Sorry for the questions but the cache pool is not quite the picture I had in my head and so I want to know what it can do and what to expect from it for drive failures or other issues.

 

Thanks for the help and info

There was some discussion over here. Don't know of anybody that has posted about success.

Cache pool is too new here at unraid to answer most of those questions from experience, however a little googling can find answers in other linux systems.

2. AFAIK, that command tells the BTRFS driver to spread the data amongst all member devices and make sure there is at least 2 copies of each bit (RAID1) so yes, it's valid for any number of devices >1.

3. BTRFS is a strange beast, it's concept of RAID1 is more flexible than most traditional RAID1 systems. Bottom line, there is a complex set of rules that determine what you can and can't do with removing and adding devices to a pool and not lose data. Theoretically as long as your total data stored on the pool is small enough to enable 2 copies amongst all the member devices, you can mix and match sizes, add or remove devices, run a balance command, and it will heal the pool.

 

The issues we currently seem to be having is with going below 2 devices, I was unable to figure out a method to break a RAID1 and use the remaining device as a healthy single cache drive without manually mounting it as a degraded RAID1. It probably would have been perfectly happy to replace the second device with another and rebuild using the balance command, it just didn't like downconverting from RAID1 to single.

Thanks for the fast replies,

So reading your link trurl posted am i assuming you cant replace a drive unless it fails and Unraid boots it off the pool?  I understand its new and like others Im still trying to understand what can be done.  In the end I think I might rebuild the pool with just two drives.

 

Is my first question an issue or could it be the reason why I am not able to replace a drive?

1. When looking at the Balance Status both say “No balance found on '/mnt/cache'”, is this normal?  If not what is normal?

I think this is normal. At least, that is what mine says and it has been working fine for several months.

Thank you