[Solved]LVM2 and XFS - zero unused blocks

[lyallp]

Anyone know of a tool whereby I can zero unused blocks on XFS filesystems?

I am running XFS natively on root and /boot but all my other filesystems are within LVM2.

The reason I want it is that I am building a Gentoo Virtual Machine in VirtualBox and want to, eventually, be able to compact the Virtual Disk.
Initially, I would compact with cp --sparse=always, but when VirtualBox fixes it's compact code (apparently, it's broken in 2.2.2) , I would use that.

Any assistance is greatly appreciated.

[forkbomb]

I've heard of people zeroing or erasing unused space with dd using various special /dev nodes (/dev/random, /dev/urandom, etc).

dd if=/dev/zero of=/my.output.file && rm /my.output.file

It'll run out of space eventually and then be removed.

Or am I reading the question wrong?

EDIT:
Might also want to run sync after the outfile has run out of space and before you remove it.

Here's somebody doing something similar with VMware images:
http://h0bbel.p0ggel.org/shrinking-vmdk-files

[lyallp]

You read my question quite accurately.
Yes, this will work but I was hoping there may be the XFS equivilent of Microsofts 'sdel' command, which has a 'clear unused space' option.
This may do the job, so long as VirtualBox does not allocate space if zeros are written to it, otherwise, I can expect my disk to fully expand out, prior to me shrinking it.

Thanks.

[lyallp]

FYI: VirtualBox did not extend the vdi storage when I filled up each of my file systems in the VM.
Subsequent

Code: Select all

VBoxManage modifyhd --compact DISK-GUID

compacted my disks by around 15% (about 1G off of a 7G image).

[forkbomb]

FYI: VirtualBox did not extend the vdi storage when I filled up each of my file systems in the VM.
Subsequent

Code: Select all

VBoxManage modifyhd --compact DISK-GUID

compacted my disks by around 15% (about 1G off of a 7G image).

Good to know for future reference. Thanks for the necrobump.

[Shining Arcanine]

I've heard of people zeroing or erasing unused space with dd using various special /dev nodes (/dev/random, /dev/urandom, etc).

dd if=/dev/zero of=/my.output.file && rm /my.output.file

It'll run out of space eventually and then be removed.

Or am I reading the question wrong?

EDIT:
Might also want to run sync after the outfile has run out of space and before you remove it.

Here's somebody doing something similar with VMware images:
http://h0bbel.p0ggel.org/shrinking-vmdk-files

The meta data involved in doing that will not be zeroed, but that is probably good enough.

[kernelOfTruth]

FYI: VirtualBox did not extend the vdi storage when I filled up each of my file systems in the VM.
Subsequent

Code: Select all

VBoxManage modifyhd --compact DISK-GUID

compacted my disks by around 15% (about 1G off of a 7G image).

nice find !

thanks !