Please help me understand my used space

The OS of the NAS is saved on the drives, so basically it takes up some space. Also, considering that the drives themselves have their own firmwares , it will also take some space.

Drive firmware is in the drive flash memory, not on the platter. And df /data only reports on the data partition, so it does not include the OS partition.

mrQQ - you are running OS6 on this ultra, correct?

With BTRFS there are a lot of reasons why these numbers might not tie out. I think by default there are two copies of the metadata on the disk, which I think is enough to account for it (esp. if checksums are turned on). You might also add -a to the du command, and make sure it is counting the data in the hidden folders of the \data root.

In addition, snapshots/CoW create a discrepancy (though in the other direction - du reports more than df). Folder compression will also create a discrepancy (again in the other direction).

With BTRFS you would want to use e.g.

# btrfs fi df /data

Yes, that will give you more information than df. If you want to compare with df, you might want to add -k to use KiB units.

# btrfs fi df /data -k

StephenB wrote:
Drive firmware is in the drive flash memory, not on the platter. And df /data only reports on the data partition, so it does not include the OS partition.

only /data /home and /apps are shown to be located on /dev/md127? /home and /apps take almost nothing, definitely not 200GB!

StephenB wrote:
mrQQ - you are running OS6 on this ultra, correct?

yes.

StephenB wrote:
With BTRFS there are a lot of reasons why these numbers might not tie out. I think by default there are two copies of the metadata on the disk, which I think is enough to account for it (esp. if checksums are turned on). You might also add -a to the du command, and make sure it is counting the data in the hidden folders of the \data root.

-a says that cannot both summarize and show all entries?

StephenB wrote:
In addition, snapshots/CoW create a discrepancy (though in the other direction - du reports more than df). Folder compression will also create a discrepancy (again in the other direction).

what is CoW? how do I see space taken by snapshots?

mdgm wrote:
With BTRFS you would want to use e.g. # btrfs fi df /data

this shows:

root@nas:~# btrfs fi df /data -b
Data, single: total=1914870562816, used=1771504107520
System, DUP: total=8388608, used=208896
System, single: total=4194304, used=0
Metadata, DUP: total=40265318400, used=1986809856
Metadata, single: total=8388608, used=0

so it still shows that 1.7tb is used, and only 2gb metadata. So where are those 200GB?

Maybe it would help if I could take a look (sent you a PM about this) and/or if you can send me your logs (see The Sending Logs link in my sig). Probably easier than asking for a series of commands.

Looks like you have a lot of metadata.

I wonder if you are using snapshots. In the web interface you should see any snapshots when you go to Shares and look at the Timeline.

Also, did you confirm that du was processing the hidden files in \data (in particular \data\.apps)?

Note that existing snapshots are not deleted when you turn them off.

I deleted snapshots manually.

I would like to believe du shows correct info, as that is exact same thing I see when looking via samba at /data (as i've said, .apps is around 350MB).

mdgm wrote:
Maybe it would help if I could take a look (sent you a PM about this) and/or if you can send me your logs (see The Sending Logs link in my sig). Probably easier than asking for a series of commands. Looks like you have a lot of metadata. I wonder if you are using snapshots. In the web interface you should see any snapshots when you go to Shares and look at the Timeline.

I will let you have a look, indeed will be much faster.