Strange fragmentation in nearly empty filesystem

[Eric Sandeen]

Carsten Oberscheid wrote:
> Hi there,
> 
> I am experiencing my XFS filesystem degrading over time in quite a
> strange and annoying way. Googling "XFS fragmenation" tells me either
> that this does not happen or to use xfs_fsr, which doesn't really help
> me anymore -- see below. I'd appreciate any help on this.
> 
> Background: I am using two VMware virtual machines on my Linux
> desktop. These virtual machines store images of their main memory in
> .vmem files, which are about half a gigabyte in size for each of my
> VMs. The .vmem files are created when starting the VM, written when
> suspending it and read when resuming. I prefer suspendig and resuming
> over shutting down and booting again, so with my VMs these files can
> have a lifetime of several weeks.

I would suggest using xfs_bmap to look at the file layout, it will be
much more informative than filefrag.

I don't know how vmware is writing the files out (I don't use vmware, so
can't test) but I'd suggest looking at xfs_bmap output when it's first
created, and then also when it's first written (but perhaps before it
gets too horribly fragmented).

The first question I'd ask is whether it's a swiss-cheese looking sparse
file with many holes.

-Eric