Let me say I'm pretty new to linux filesystems, and know practically nothing about btrfs, other than it does sort of an ad hoc duplication of data across multiple drives for redundancy.  It would appear to have some configuration as to how many copies of the data it should strive for.  My question is, is it possible to make this setting on a per folder basis?

Here's my use case.  I've got a dvr/media server (SageTV, plus others), and the cache is used for recordings as well as appdata, and some vmdisks.  I have 2 disks in my cache pool, which of course duplicates everything to both disks.  I don't have a real need for the recordings to have this redundancy, however, and would be perfectly fine if it was written to just a single disk for the short time it resides there before mover pulls it off and throws it onto the array.  The recordings are going to their own share, so they exist in a specific folder on the btrfs cache drive.  Is it possible to set btrfs to not care about duplicating data in that folder?

Why not just make that share cache-no?

Because I do need the performance benefit of the cache, especially when recording 5 or 6 hd channels at a time while watching a couple others due to the seek-time cost, just don't need to write it to both SSDs.

Edited March 5, 20179 yr by CraziFuzzy

Maybe use a separate Unassigned Device then. Of course, you would have to handle moves to the array manually or with a scheduled script.

3 minutes ago, trurl said:

Maybe use a separate Unassigned Device then. Of course, you would have to handle moves to the array manually or with a scheduled script.

Could you not do this but map it to a directory on the cache drive as a symlink/hardlink and let mover do it?

I don't have a real desire to add another SSD to the system, just to handle the recording shares, when there are already two there doing very little.  Was just trying to make things a little more efficient.

9 minutes ago, CraziFuzzy said:

I don't have a real desire to add another SSD to the system, just to handle the recording shares, when there are already two there doing very little.  Was just trying to make things a little more efficient.

Fair enough.  I would like to know if my suggestion is possible for me however.

6 hours ago, BobPhoenix said:

Fair enough.  I would like to know if my suggestion is possible for me however.

I'm guessing it might work, but there might be issues with drive space checks on the cache, though I don't know what those issues might be.  I'm guessing it simply checks the free space as reported by the mount point, so free space on the unassigned drive would be ignored.  I suppose it wouldn't hurt to try it out a little if you do have an extra SSD laying around.

I do know that mover deletes a folder from the cache when it's moved everything out of it.  This is typically good housekeeping, so there aren't empty folders laying about on the cache drive.  I don't know if this would affect the mount point of your unassigned device or not.  I'm guessing mover would just end up with an error when it tried to delete the folder.

I think the potential issue, is that when a file is opened for writing to a share that has cache enabled, it will first check the free space on the cache, and if the free space is greater than the leave free setting, it will open the file on the cache.  If free space is not greater than the leave free setting, it will open the file directly on the array.  If it does this check in the destination folder of the cache drive, it likely will work just fine, because it will be checking the space of your unassigned device.  If, however, it just checks the root of the cache drive for the free space, then it may very well think there is space there, but the unassigned device may actually be full.  This would cause unRAID to still try writing to the unassigned device, and the write would simply fail because there is no space for the recording.

All good thoughts and some of why I hadn't tried it yet.  To be honest I was going to put a spinner mounted that way and it would be 2TB minimum so I'm not worried about running out of space as I would have it move daily and even with 10 Tuners running at a time it still takes me about 360 hours to record 2.75TB of recordings currently.  The space calculation issue and more importantly the deletion of folders was what I was worried about most.  May have to modify the mover script to do something about the folders.  Also why up until recently I've only thought about separate recording drives mounted with "Unassigned Devices"  separate from my cache drive.  But I have ONE SageTV VM that this would be perfect for since it only has 4 tuners and only records 12 shows a day and only a max of 3 simultaneously.

Edited March 6, 20179 yr by BobPhoenix