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I have been working at this small business for over a year. We have one ReadyNAS4312. It is RAID-6 with 32.7 TB, 12 disks, and X-Raid is on. (I'm just reading about X-Raid). ReadyNAS is showing 3.64 TB free.
To get to the point, can I ignore ReadyNAS log warnings on 10% free space if storage is fixed and pre-allocated -- by 2 mounted LUNs containing 2 VHDX files/volumes, used for another virtual appliance -- such that no other data will be written to this RAID outside of the pre-allocated volumes?
We had one SCSI-LUN allocated to a Hyper-V VM Host for Unitrends backup. It had one 17.5 TB VHDX volume/disk mounted in LUN -1.
I think more disks were purchased at some time, but no more space had been allocated to Unitrends by previous IT persons.
I created a 2nd SCSI-LUN on this ReadyNAS and another 13.1 TB VHDX volume created on LUN-2. I don't remember all the steps, but I figured it out and it has been working since July 2021, so 1.5 years okay. ;
Following procedures, I didn't have to erase disks and create a single virtual disk for Unitrends. Unitrends virtual appliance imported the 2nd volume to see it as one volume in its system.
That disk space as per Unitrends interface is only half-utilized, half-free, but ReadyNAS4312 is reporting:
Volume: Less than 10% of volume data's capacity is free. data's performance is degraded and you risk running out of usable space. To improve performance and stability, you must add capacity or make free space.
My reasoning at the time was that since I was creating these fixed volumes -- not dynamic VHDXs -- no other data is written to this RAID outside of these Virtual Disks inside the LUNs -- then I might as well maximize capacity available to Unitrends by creating a large VHDX in the 2nd LUN. SEE PICS attached.
Now I'm concerned that I could possibly be hampering RAID capabilities by over-utilizing capacity of the ReadyNAS device.
If this warning only means I could run out of disk space if I we were to begin adding storage data outside of these pre-allocated volumes, then everything is good.
If not, I need to shut down the Unitrends appliance and shrink the 2nd VHDX so I can shrink the LUN. If that's possible without destroying data.
BTRFS needs some headroom to operate, so using any more of the free space is not recommended. If no users are writing to anything other than the static-sized iSCSI LUN's, then you are probably OK with a 10% margin. The NAS has no way of determining how much of the LUN you are using. It shows all of that space as used since, to it, it is, and that space does not count toward the desired BTRFS headroom.
BTRFS needs some headroom to operate, so using any more of the free space is not recommended. If no users are writing to anything other than the static-sized iSCSI LUN's, then you are probably OK with a 10% margin. The NAS has no way of determining how much of the LUN you are using. It shows all of that space as used since, to it, it is, and that space does not count toward the desired BTRFS headroom.
