Replace cache drive with another data disk?

[master.h]

I've searched through the forums, and can find all sorts of info regarding using unraid without a cache drive, but I couldn't seem to find exactly what I was looking for. I am in the process of building an unRAID Plus server that is going to be an off-site backup for my main system. Since it's not actively going to be used, I plan on not using a cache drive. However, I don't have an option to replace the cache drive with a "disk 6." I can only start the array with parity and 5 data drives. Do I lose out on the 7th drive unless I'm using a cache drive?

[garycase]

Some time ago, Tom made the following comment:

 

Tom -- I noticed the "Plus" key now says "support up to 7 hard drives"  (up 1 from the previous 6)

 

Does it also support a cache drive?  .. or is the cache one of the 7?

 

More precisely, does this mean a Plus system can have parity plus 6 data drives?

Currently in 5.0-rc, Plus supports 6 array drives (parity + 5 data), plus the Cache drive, and also does not support Active Directory.  Release 5.0 "final" Plus will support 7 total drives and have no other restrictions (and Basic will support 3 drives with no other restrictions).  So yes, Plus could have parity + 6 data drives.

 

Clearly his comment, "Plus could have parity + 6 data drives" does not match the actual implementation.  I'll send Tom a note with a link to this thread -- hopefully he'll post a response.

 

[Oddwunn]

SQDV (same question different version): I have 2 Pro licenses and I recently upgraded to 5.0 release. In 4.7, I had 20 disks + parity + cache for assignable "slots". I do not use a cache drive at all, so I never used the cache slot. Now that I switched to 5.0, I now have 23 disks + parity + cache. Is there any way to convert the labeled "cache" slot to a 24th "data" slot or otherwise use that slot to store data? IOW I would like to have 24 data disks + parity if that is possible. Or, if that is not possible, is it possible to use the cache slot to store data even if it is not protected by parity?

[mikejp]

Is there any way to convert the labeled "cache" slot to a 24th "data" slot or otherwise use that slot to store data? IOW I would like to have 24 data disks + parity if that is possible

 

What he's asking...

[master.h]

Or, if that is not possible, is it possible to use the cache slot to store data even if it is not protected by parity?

 

Yes, you can store data on your cache drive, and it is not protected by parity. Lots of people use their cache drive to store the settings/data for the various plugins. I use my cache drive to store the data for Plex and Transmission. Sure, I lose that stuff if my cache drive fails, but it's not really data I'm concerned about keeping. It's no big deal to me to put a new cache in and let those apps repopulate the data.

[garycase]

Okay, I've heard back from Tom.    As you noticed, v5.0 has not, in fact, allowed the cache drive to be used for data instead on either Plus or Pro.

 

That's because of the way in which that was going to be possible => it depends on the btrfs "cache pool" feature that was originally planned for v5.0    Obviously that did not get implemented.

 

WHEN btrfs is implemented, then you'll be able to assign a drive as either data or "pool" ... which essentially means you can have a number of cache drives (in a fault-tolerant btrfs array), or you can use all the drives for data (protected by the traditional parity drive).    So Plus can have 6 data drives; and Pro can have 24 once that's implemented.

 

It's not clear, however, just when that will be -- and I hesitate to guess.    But it IS coming in a future "point release"  (i.e. v5.1,  v5.2,  etc.)