How to determine the reserved blocks in xfs filesystem ?

[Brian Foster]

On Tue, Nov 18, 2014 at 06:05:58PM +0530, Mukul Malhotra wrote:
> ​Hello,
> 
> Does xfs have reserved blocks too, like ext* ? if yes, how can they be
> determined ?​
> 

XFS reserves blocks internally such that it can perform operations when
all free space is consumed, etc. It looks like 5% is the default.

I don't think it's "like ext4," however, which reserves blocks for the
root user. I don't believe the reserved blocks in XFS are accessible for
file allocation by any user unless the reserve pool is modified as such.

> Can you provide the specific command.
> 

The following command can get/set the reserved block count on an active
mount:

xfs_io -x -c "resblks" <mnt>

Note that this can lead to problems if reduced too much and all space is
consumed, as sometimes block allocation is required to perform space
freeing operations (removing a file, etc.). This is probably a reason
the resblks command is only available in xfs_io expert mode. ;)

Brian

> Thanks
> Mukul

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