Re: [Xen-users] Clean deleted space in linux diks?

[James Pifer <jep@xxxxxxxxxxxxxxxx>]

> IIRC the easiest way to do this with zfs-based SAN is to just enable
> compression, and then write zeroes. zfs will treat zero-blocks
> specially, using no space at all to store them. However that only
> works when there's no snapshot/clone. If there's snapshot, old
> snapshot may still refer to the original non-zero block, thus no space
> is freed until I delete the snapshot/clone.
> 
> If the SAN uses some virtual disk format (e.g. VDI, VMDK) to store
> block device, the "reclamation" process must be done manually after
> you zero-out the blocks.
> 
> So again, it depends on how the SAN does reclamation process.

I'm not exactly sure how their reclamation process works. They say I
have to zero out the space, then their reclamation should recover it. No
snapshots involved. So my question, should this command zero out the
space?
cat /dev/zero > null-file ; rm null-file

Thanks,
James


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