[COMPLETE] BTRFS Cache Pool - config question

[Jcloud]

Hello, first post and new unRAID user, sorry to clutter forums with newb question.

 

First off, if unRAID devs are reading this, with the inclusion of hyper-visor stuff of version 6, THANK YOU -- this is the kind of OS I've been waiting for probably 5-10 years. Thank you for your hard work.

 

Here's the setup and the question:

Currently, I have a 120GB SSD and a 2TB HDD setup as my cache pool. The file system configuration is default, so it setup a BTRFS-raid1 setup (I get that). For pool size it says it has 1TB of space (OK it cut my 2TB HDD in half and "mirrored" it) -- I get that too. My question is what has happened to the SSD space? Is my cache pool and BTRFS working like a hybrid-HDD? I.E. stuff that gets used a lot ends up on the SSD and the less used data gets shuffled to the HDD?

 

Label: none  uuid: 10088bff-15b3-4934-ae6e-3ee235845624

Total devices 2 FS bytes used 640.00KiB

devid    1 size 111.79GiB used 3.03GiB path /dev/sdb1

devid    2 size 1.82TiB used 3.03GiB path /dev/sdd1

 

btrfs-progs v4.1.2

btrfs filesystem df:

Data, RAID1: total=1.00GiB, used=512.00KiB

System, RAID1: total=32.00MiB, used=16.00KiB

Metadata, RAID1: total=2.00GiB, used=112.00KiB

GlobalReserve, single: total=16.00MiB, used=0.00B

 

What I would like is a FAST storage pool (don't need anything like RAID0 or RAID0 with SSDs) for VM and primary steam library location. Would I get better speed performance moving the 2TB HD to my array and leave the cache strictly as SSD?

 

Thank you for your time and replies.

[trurl]

I think the 120 is probably there but it isn't obvious with the way drive manufacturers label their drive capacities and the way things get calculated and rounded for display.

 

The drives are not handled separately as far as unRAID is concerned. That is all up to btrfs so I think you are mostly going to see performance similar to the spinner for your configuration.

 

I would just take the 2TB and put it in the array, and later add another 120 SSD for a mirror. They are pretty cheap these days. I have 2 x 120GB SSDs for my cache pool. If you aren't going to be caching a lot of user share writes every day you will probably be good with that. I don't cache any user share writes and just use my cache for dockers.

[Jcloud]

Thanks for the reply, I think you answered the crux of my question.

 

I'll leave the post open for a day or two -- if someone else wants to add their two cents. Afterwards I'll edit my post to add COMPLETE to subject line per forum stickies.

 

 

[JorgeB]

You can’t rely on displayed free space when using 2 different size disks for cache pool, it should show 1.06TBs, but using default settings you can only use up to the size of the smaller disk, i.e., when you reach 120GB used space you won’t able to copy any more data to the cache pool, so you’ll be wasting almost 2TBs.

[Jcloud]

Alright 2TB re-purposed for array, and I'll just have to wait for next year for SSD-dollar/gb to jump down again.

 

Thanks for the info.