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Forum Discussion
Disk Space - Usage doesn't match actual
Hi,
ReadyNAS 102, v 6.2.4
df -h
returns:
Filesystem: /dev/md127 Size: 1.9T Used: 1.7T Available: 186GB Use %: 91% Mounted on: /data (and also repeated for /home, /apps, /run/nfs4/data/Recordings, /run/nfs4/data/home /var/ftpBackup)
So, showing that I am using 1.7TB of my 1.9 = nearly full.
However this isn't reflective of actual usage.
du -sh *
returns:
87M apps 5.7M bin 4.0K boot 873G data 4.0K dev 4.3M etc 24M frontview 0 ftp_ban.tbl 0 homes 36M lib 16K lost+found 0 media 4.0K mnt 5.1M opt du: cannot access `proc/21012/task/21012/fd/4': No such file or directory du: cannot access `proc/21012/task/21012/fdinfo/4': No such file or directory du: cannot access `proc/21012/fd/4': No such file or directory du: cannot access `proc/21012/fdinfo/4': No such file or directory 0 proc 32K root 1.2M run 7.9M sbin 4.0K selinux 4.0K srv 0 sys 28K tmp 211M usr 211M var
The only thing of any size is /data which is 873GB
So the overall disk usage should be maybe about 1TB, not 1.7TB
The fact the filesystem /dev/dm127 is mounted repeatedly on /home, /apps, /run/nfs4/data/Recordings, /run/nfs4/data/home /var/ftp/Backup -- I don't think this should be an issue as it's just different mount points for the same data, right? (the contents of /data/home is the same as /home for example).
So then I'm trying to figure out what on earth is taking up all the additional space.
Wondering if it's part of the auto backups (snapshots) but surely these would auto purge (over time and also hopefully when it gets close to full), and surely these would be incremental therefore not taking up an additional 700+GB
Any pointers, most welcome.
Thanks
Rob
11 Replies
Replies have been turned off for this discussion
Hello,
Please try the btrfs related commands to display space used/free. A good explanation of the commands can be found in the btrfs wiki:
https://btrfs.wiki.kernel.org/index.php/FAQ#How_much_free_space_do_I_have.3F
You can post the results of
# btrfs fi show /data
and
#btrfs fi df /data
here if you wish.
Bye,
Eskender
du is not designed for calcluating usage on the BTRFS filesystem. Whereas the BTRFS related commands EskenderNG mentioned are.
You should be using the btrfs commands for this type of analysis.
Generally the discrepancy comes from two basic sources.
One is that du doesn't account for btrfs metadata. With ext, metadata is saved in inodes, which are preallocated when the file system is created. BTRFS doesn't do that, and the amount of metadata space used is dynamic.
The other is that du ignores snapshots. Given the size of your discrepancy, I am guessing you have snapshots enabled. You should delete some of them from the web UI to free up space. One approach is to delete all the snapshots from shares that have a lot of churn (changed or deleted files - not adds or renames). Another is to delete the oldest snapshots from each share.
The way to clean up metadata is to schedule regular balance jobs (system->settings->maintenance). I run that quarterly, but if there a lot stuff changing on your NAS you might want to schedule it monthly.
Hi,
Thanks for your replies.
btrfs fi show /data Label: '0e36d6d7:data' uuid: 4325b83e-28ce-4f63-9e46-a5b09379d96b Total devices 1 FS bytes used 1.63TiB devid 1 size 1.81TiB used 1.64TiB path /dev/md127 btrfs fi df /data Data, single: total=1.64TiB, used=1.63TiB System, DUP: total=8.00MiB, used=224.00KiB System, single: total=4.00MiB, used=0.00B Metadata, DUP: total=2.00GiB, used=1.29GiB Metadata, single: total=8.00MiB, used=0.00BSo yes here we're seeing the full 1.7T usage.
The meta data is small enough so are we good to presume this is caused by snapshots?
Seems crazy that the snapshot system is choking the drive, essentially only allowing me to use half of the disk space as it then uses the same again for snapshots.
I currently don't have access to the GUI (remote ssh only) so is there a way I can clean things up through SSH?
Also when I've tried to clean up old snapshots through the GUi before it's an absolute pain as you have to go into each one and delete, wait, repeat, which can be very laborour if you're looking at days/weeks/months. And ideally I don't want to be having to clear through them periodically. Is there a way to a) reduce the frequency of snapshots and b) make it auto purge the oldest if disk space gets beyond, say 80%?
And, is there a way to do any of this via SSH, as I won't have access to the GUI for a few weeks, and by then it'll probably hit 100% at this rate.
Thanks heaps again,
Rob
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