Drives, Partitions, Volumes
Windows storage explained
A quick primer on what is what in the Windows storage framework.
When it comes to storing data, Windows
operates with several elements of the storage "stack":
At the hardware level there are physical drives
provide a pool of raw storage space, which can be read and
written in fixed-sized chunks called sectors
Drives can be sliced into partitions
Partitions then can be formatted to host a file system
which enables reading and writing data as arbitrary-sized
, grouping them into directories and generally
managing them in various ways.
Formatted partitions are called volumes
As you may know, physical drives may be bunched together
to form a single storage facility called
RAID looks like just another drive to its host computer,
but on the inside it routes read/write requests to one
or more drives to provide for extra speed or to ensure
data redundancy (or both).
RAID is a very broad and interesting topic worthy of
its own post, but the key takeaway is that RAID is
a hardware abstraction - it talks and works like
a single drive.
However, there exists one case where we want to actually
ignore this abstraction and talk to each of the RAID drives
That would be the case of assessing health status
the array by analyzing individual drive's
Volumes do not have drive letters attached to them
by default as they are merely partitions that were marked
up for storing files.
To make volumes actually accessible from Windows, they
need to be mounted, which is a process of either
assigning a drive letter to the volume or "pinning"
it to a directory on another, already mounted, volume.
On Windows, when a new volume is created, the OS will
mount it automatically to the one of available drive
letters. It will also do the same when a removable drive
is plugged into the system.
In other words, the mounting step is present
on Windows, but it's conveniently obscured by the OS.
One aspect of the storage layering that commands a
closer look is the relationship between partitions
In the simplest (and most common) case, this relationship
is 1:1 - each partition is formatted to yield a volume.
However, it's possible to combine multiple partitions of
the same drive into a single volume, called a
simple dynamic volume
It's also possible to build a volume out of several partitions
on different drives
, creating a so-called
spanned dynamic volume
These types of volumes are populated sequentially, one partition
at a time. Their purpose is to allow growing / shrinking volumes
as your data storage needs change.
Furthermore, Windows also supports a so-called Software RAID
which is an arrangement of partitions that mimics the semantics of
levels 0, 1 and 5 of conventional (hardware) RAID.
volumes distribute read/write requests
between several equally-sized partitions on different drives,
improving the overall throughput rate.
volumes provide data redundancy by writing
same chunk of data to all partitions in the volume in parallel.
Windows also supports a software equivalent of
however a thing to note here is that the prevailing professional
opinion is to use any software RAID only as an option a last resort.
The one true RAID is the hardware one.