Hi,

 

After doing a search of the FAQ and the forum, I have some questions about swapping out cache drives.

 

I am currently running unRAID 6.2 stable release.

 

My BTRFS cachce currently consists of the following SSDs:

1. 256GB (originally started with just one)

2. 256GB (added it to have redundancy)

3. 512GB (added it later, figuring to double the size of usable space to 512GB)

 

The webGUI always reports having only 256GB available and shows only the two 256GB with used space; the 512GB appears to be have no read/writes to it.

 

I want to swap out the two 256GB SSDs with a single 512GB SSDs, resulting in two 512GB SSDs.

 

Here's my questions:

1. Would the fastest way to do this be to backup everything on the cache drives to a non-cache drive; remove all the drives from the cache pool; physically swap out the two 256GB for the second 512GB drive; re-create the cache pool; and copy the data back to the new cache pool?

 

2. Do I need to somehow clear out/reformat the old 512GB drive before re-creating the cache pool?  I've seen references about using preclear on a drive before using it for cache to make sure it is empty; but, also have read other messages saying preclear is for hard drives only.

 

3. I've read that having a cache pool using different size drives could result in incorrect cache pool space being reported in the webGUI.  If I was to add a third drive of equal size (e.g., a 3rd 512GB drive), will this result in 750GB usable?

 

Thanks,

Marcos

 

Have you tried a rebalance operation?  That might straighten it all out.

After the balance click on "cache" and post the info on "btrfs filesystem show".

Thanks for the replies.

 

After doing the balance operation, btrfs filesystem show:

 

Label: none  uuid: 12f30176-f0de-42b0-aab8-e77c658765ef

Total devices 2 FS bytes used 86.35GiB

devid    1 size 232.89GiB used 99.03GiB path /dev/sdb1

devid    2 size 232.89GiB used 99.03GiB path /dev/sda1

 

It doesn't show the 3rd device, a 525GB SSD.  I never noticed this before.  If I use the arrow keys on the cache display, I can see a screen for cache3 for the 34d device.

 

Any suggestions on how to get that device recognized as part of the cache pool?  Given btrfs filesystem show does not list the 3rd SSD, can I simply remove it and add it back?

Don't know.  Try it!

Like you suspected cache3 is not being used, this can be tricky to fix, first thing to do is to backup your cache, then you can try:

 

-remove cache3, SSD has to physically disconnect from the server (or precleared) or cache will probably show unmountable.

-if it works OK with cache1 and 2, try to re-add cache3, but you'll need to preclear it first.

 

You can always check if all is well by looking again at btrfs filesystem show.

I will try removing/pre-clearing/re-installing that 512GB SSD.  Just to be sure: preclear SSD drives is fine?  Old forum messages about preclear being bad for SSD is not true?

 

Sent from my SM-G930T using Tapatalk

 

 

It's fine, it's the same as SSD preconditioning, though you should only do it when necessary.

Thanks for the confirmation about preclear.

 

I'll give it a try and report back.  Might have to wait until middle of next week due to work.