StorNext: File System Free Space Shows More Space Consumed Than Disk Usage Indicates

StorNext: File System Free Space Shows More Space Consumed Than Disk Usage Indicates ("du" and "df" Outputs Differ)


Symptom:
File system free space shows more space consumed than disk usage indicates in a StorNext File System. There are few, if any, sparse files.

Cause:
On heavily used file systems, ones with many files added and deleted, the free space fragmentation can exceed 1,000,000 fragments. The current ABMFreeLimit calculation only returns the first 1,000,000 fragments back for reuse. The ABMFreeLimit parameter instructs the file system manager how to process the Allocation Bit Map, which in turn goes into the calculation of the file system free space.

You can verify this condition by searching cvlog for the following line at file system startup:

[0403 10:31:07] 0x47a39940 (Warning) FSM Alloc: Stripe Group DataFiles1 2821207422 free blocks in 1685714 fragments ignored.

Action:
To solve this problem, change the following in the Global Parameters section in the file system configuration file (/usr/cvfs/config/<fsname>.cfg).

ABMFreeLimit YES

The default for this parameter is set to NO. After you enable this setting, StorNext will use the previous method of calculating the free space by considering ALL fragments, not just the first one million. However, a tradeoff occurs, since the FSM will consume more kernel memory and may take longer to fail over.

Audience: 
Public Unrestricted
Review/Evaluate: 
2015-10-15
Document Type: