The number of disks in the volume (a volume can span multiple disks).
An extent is a contiguous run of sectors on one disk.
so is a partition. What's the difference? None from the grouping of sectors stand point. An extent is a partition. It might not be created in MBR or PBR, but it is still a partition: a contiguous collection of sectors. If you really want to get technical, then we have to say that it is a sub-partition. But a sub-partition is a partition: a collection of contiguous sectors.
That's what goes for Microsoft.
Now on to Linux:
Anatomy of LVM
3.2. physical volume (PV)
A physical volume is typically a hard disk, though it may well just be a device that 'looks' like a hard disk (eg. a software raid device).
Here the disk is assigned to the volume. The volume is made out of disk (1).
This also says that from a volume stand point, anything that "looks" like a disk is fair game. It will accept it as a component of the volume.
3.3. logical volume (LV)
The equivalent of a disk partition in a non-LVM system. The LV is visible as a standard block device; as such the LV can contain a file system (eg. /home).
Here, the volume is clearly what gets "formatted", just like a regular old partition. That's all it says, it does not define what a logical volume is, but we will get a better understanding in 3.6. We can however deduce that a logical volume is what the OS will see as "the storage".
3.4. physical extent (PE)
Each physical volume is divided chunks of data, known as physical extents, these extents have the same size as the logical extents for the volume group.
Each hard disk (or raid) is divided (there is a word missing here, I will assume it is "into") chunks of data, known as physical extents. We saw in the first definition that: "An extent is a contiguous run of sectors on one disk." Disks are divided into sectors. Sectors are grouped for use by file systems. In FAT, they are grouped into clusters. In Linux Logical Volume Management, they are grouped into physical extents. Physical extents are clusters of sectors. A physical extent is a sub-division of a physical volume which is anything that will behave as a group of contiguous sectors (disk, partition, ...).
3.5. logical extent (LE)
Each logical volume is split into chunks of data, known as logical extents. The extent size is the same for all logical volumes in the volume group.
We saw previously that term logical volume (LV) has still not been defined up to this point. It is still the case here.
3.5 tells us that each volume is logically split. That logical subdivision is called a logical extent. So, we could say that a logical volume is a container of logical extents. A logical extent is a sub-division of a logical volume.
Logical Volumes are made from either whole disk and/or partitions, but you can only access portions called logical extents. So, looking at extents, you will find them in a volume, and, looking at disks or partitions, you will also find them in a volume. The volume is the “thing” that "holds" both. This is just like extended partitions and sub-partitions. Extended partition is the container for sub-partitions. Sub-partitions are inside extended partitions. Extents are inside volumes.
Physical extents (clusters of sectors) are inside physical volumes (disks, partitions ...).
Logical extents (storage units) are inside Logical volumes ("the storage").
3.6. Tying it all together
A concrete example will help:
Let’s suppose we have a volume group called VG1, this volume group has a physical extent size of 4MB. Into this volume group we introduce 2 hard disk partitions, /dev/hda1 and /dev/hdb1. These partitions will become physical volumes PV1 and PV2 (more meaningful names can be given at the administrators discretion). The PV's are divided up into 4MB chunks, since this is the extent size for the volume group. The disks are different sizes and we get 99 extents in PV1 and 248 extents in PV2. We now can create ourselves a logical volume, this can be any size between 1 and 347 (248 + 99) extents. When the logical volume is created a mapping is defined between logical extents and physical extents, eg. logical extent 1 could map onto physical extent 51 of PV1, data written to the first 4 MB of the logical volume in fact be written to the 51st extent of PV1.
3.1. volume group (VG)
The Volume Group is the highest level abstraction used within the LVM. It gathers together a collection of Logical Volumes and Physical Volumes into one administrative unit.
VG Administrative unit = collection of Logical Volumes and Physical Volumes
VG Administrative unit = collection of Logical Volumes (disk partitions) and Physical Volumes (hard disks)
Tying it all together:
In this example, we're creating a volume group called VG1 (with physical extent size defined as 4MB)
hard disk partition /dev/hda1 = PV1 => placed in VG1 (seen as hard disk)
hard disk partition /dev/hdb1 = PV2 => placed in VG1 (seen as hard disk)
VG1 = PV1+PV2
VG1 extent size = 4MB => (PV1+PV2) are divided up into 4MB chunks (kind of like FAT clusters)
PV1/4MB = 99 extents
PV2/4MB = 248 extents
VG1 = PV1+PV2 = 99+248 = 347 extents
LE (logical extents) = blocks of logical volume
PE (physical extents) = blocks of the disks or partitions
L VOLUME = what's accessible from the OS = subdivided in LE(s) = group of LE(s) = container of LE(s)
LE(s) are in LV(s)
LE(s) are mapped to PE(s) which are groups of sectors.
sectors go into PE. Each PE goes into a LE. LEs go into LV.
The volume is the container. It is a logical structure like a folder in a file system. Files go into folders, does not mean they sit on the same sector. It's a logical organization, not a physical one.
A volume is a logical structure used to contain whatever grouping of sector your OS allows (whole disk, partition, combination of disk & partition).
An article can span across multiple pages.
Article is not container of pages.
Article is content. Collection of pages are container of article.
An article is a collection of words.
Article is the container for words.
Words go into articles.
Pages hold articles.
Pages are containers for articles.
An article can span multiple pages because pages break articles into chunks. That does not change the fact that the thing called "page" was created to hold and display articles.
I still can't see how volumes don't contain partitions (contiguous blocks of sectors), regardless of what volume you look at. The sectors can come from disk or partition, but the place where they are logically grouped into a file system accessible storage is "the volume". I don't mind being wrong (in which case I will quickly adjust), but you have to show me where I'm wrong.
Good discussion so far.
Thank you all.