Forum Discussion

Tutor

Oct 13, 2016

Running defrag, losing 1GB a minute

I am running defrag for the first time in a while... and my free space is dropping like crazy. Size Used Avail Use% Mounted on 30T 28T 632G 98% /data When this started, I had over 1TB o...

Performance

mdgm-ntgr

NETGEAR Employee Retired

Oct 13, 2016

Sounds like some of your files probably use CoW.

Do you (or did you) have bit-rot protection enabled on any of your shares? This is separate to CoW but we link enabling/disabling bit-rot protection to enabling/disabling CoW.

You should free up space before running volume maintenance on a volume that is this full.

Which firmware are you running?

What does your initrd.log look like?

joe_schmo

Tutor

Oct 13, 2016

my initrd.log:

2014/01/15 14:52:32] Factory default initiated by button!
[2014/01/15 14:52:47] Defaulting to X-RAID2 mode, RAID level 5
[2014/01/15 14:53:03] Factory default initiated on ReadyNASOS 6.0.4.
[2014/01/15 14:49:34] Updated from ReadyNASOS 6.0.4 to 6.1.5.
[2014/01/15 16:02:20] Updated from ReadyNASOS 6.1.5 to 6.1.6.
[2014/04/14 05:09:27] Updated from ReadyNASOS 6.1.6 (1389750453) to 6.1.7 (1396977042).
[2014/05/24 11:33:24] Updated from ReadyNASOS 6.1.7 (1396977042) to 6.1.8 (1398980083).
[2014/10/28 16:39:30] Updated from ReadyNASOS 6.1.8 (1398980083) to 6.1.9 (1409791183).

I have Bitrot Protection (Copy on Write) enabled on all shares. Not sure wha tyou mean by Bitrot being separate to CoW since its the same option.

Firmware 6.4.2.

What's the link between what I am seeing and bitrot?

mdgm-ntgr
NETGEAR Employee Retired
Oct 13, 2016
They are not the same thing but we link enabling them/disabling them.

Running a defrag won't uncow files. It will break the CoW link between current data and snapshots, but even if not using snapshots you will see an increase in volume usage if you are using CoW.
- joe_schmo
  Tutor
  Oct 13, 2016
  Thanks for the info... have some more questions:
  
  most importantly:
  - Can I turn off CoW to regain space?
  
  And
  - Why does defragging cause space to go down, with regards to CoW?
  - How much of an increase in volume usage do I experience using CoW?
  - StephenB
    Guru - Experienced User
    Oct 13, 2016
    joe_schmo wrote:
    
    - How much of an increase in volume usage do I experience using CoW?
    
    This question is wrongly put. CoW was saving you some space, but the defrag eliminated the savings. CoW itself can only improve storage efficiency, it can't hurt it.
    
    I'm not clear on exactly why your free space is dropping that quickly with no snapshots. I am thinking there might be some that you can't see from the UI. However, your volume is extremely full, and it is also possible that the btrfs allocator is needing to grab free chunks as it defrags your files.
    
    If you purchased between 1 June 2014 and 31 May 2016, then you have lifetime chat support. You could use that, ask Netgear support to look for hidden snapshots.
    
    If there are no snapshots, then offloading some data and then doing a balance would be good next steps.