Zeroing files and free disk space
"Zero delete" function in
PeaZip's "File tools" submenu is intended for overwriting data with
all-0 stream, either as a file deletion option and as a supported mode
for overwriting partition's free space, in order to fill corresponding
physical disk area of homegeneus, highly compressible data.
Marginally, this deletion and free space optimization mode also offers
a basic grade of security over PeaZip's "Quick delete" function, which
simply remove the file from filesystem, making it not recoverable by
system's recycle bin but susceptible of being recovered with undelete
Zero deletion however is not meant for advanced security, and PeaZip's "Secure
delete" should be used instead
when it is needed to securely and permanently erase a file or sanitize
free space on a volume.
Optimize virtual disk
images with zero delete
A Disk image is a snapshot of
the content of a disk, meaning all the content of the disk is mirrored
into a file which is a 1:1 copy of the source.
This involves saving exactly the data is stored on the unit, bypassing
possible filesystem's problems or limitations, and avoiding the
inherent overhead in managing data as separate files running a set of
high level software to read the filesystem structure, which means data
recovery software may be simpler and faster.
This is usually an higly efficient way to backup large quantities of
data, and to perform a full system backup which in disaster recovery
events can be deployed without, unlike plain data backup, needing
additional work to restore the system, software, licenses etc.
But, being created in a filesystem-agnostic way, the image of the disk
contains all data featured on the unit, including ones in sectors
marked (in the filesystem) as deleted data, which may represent a
sizeable overhead - especially over the time, as files gets created and
deleted on the physical machine.
Zeroing the free space (and zeroing files being deleted) let the free
space in an higly ordered, highly compressible state, that brings
substantial improvement in terms of size reduction of resulting disk
images even with most elementary compression algorithms - often
built-in in disk imaging systems.
Consequently, it is recommended to perform PeaZip's "Zero delete free
space" on physical machines before saving disk images for
backup/disaster recovery purpose (or to routinely delete files with
Zero delete function) to substantially reduce the size of the disk
supports reading (browse, search, extract) various types of disk images
commonly used by virtualization software: QCOW2 (QUEMU), VMDK (VMWare
Virtual Machine Disk), and VDI (Oracle VirtualBox Virtual Drive Image)
often comes with non-preallocated disk image, that means the content of
of the VM is saved on host physical machine to a disk image file which
smaller than the nominal VM disks size.
Popular providers of platform virtualization solutions are Microsoft
(Azure, VirtualPV), Oracle (VirtualBox), and VMWare.
Anyway, even this optimization is often far than optimal in terms of
space occupation on host machine, as the VM disk image contains also
the data not referenced in the disk's filesystem (as explained in Disk
images paragraph), which can be a sizeable overhead over the real size
of occupied disk space inside the virtual machine, that should be the
target size for disk image - which depending on the imaging software /
VM technology may also be compressed further reducing space
As for disk images created for backup and disaster recovery purpose it
is useful having PeaZip installed in the physical machine to zeroe the
free space before the disk image creation, the same apply to virtual
machines, where PeaZip should be available and routinely employed to
zeroe the free space on VM disks, letting it in an higly uniform and
highly compressible state, which results in smaller disk image on the
host machine - which allows to more rationally use host disk space for
storing more virtual machine applicances, or more VM restore points.
External online resources: virtual machine
on Wikipedia, Microsoft
Virtual PC, Oracle VM VirtualBox, VMWare mainstream
virtualization solution providers.
Topics and serach suggestions: QCOW2 QUEMU image, VMDK VMWare Virtual
Machine Disk, VDI Oracle VirtualBox Virtual Drive Image, zero delete
files, optimize virtual
machines backup, reduce
disk image size, save disk space occupation, zeroing free
space, guest vm size
optimization, host machine disk space usage optimization, how to create
smaller disk images, overwrite data with zero, file zeroing.
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