Uses of single-partition disk configuration

Question

I see in my company's IT installations that there are numerous disks with one partition occupying all of the space on disk. There is typically something like a /dev/sdb with a partition /dev/sdb1, and the size of /dev/sdb1 is the size of the whole block device. The partition is then mounted with the required file-system format, mountpoint etc.

I do not understand why we would use a partition rather than the whole disk for such (1-partition) configurations. Is there any reason why a partition would be used in this case rather than a whole disk ? Are there any best practices that recommend this approach ?

For example, we could create a Filesystem on a whole raw block device and mount it without needing any partition:

mkfs.ext4 -E stride=16,stripe-width=64 /dev/xvde
mount /dev/xvde /mnt/abc

That creates a mountpoint without a specified partition. As a verification:

# sfdisk -l /dev/xvde

Disk /dev/xvde: 6527 cylinders, 255 heads, 63 sectors/track

# fdisk -l /dev/xvde

Disk /dev/xvde: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

For something with a partition, we get the list of partitions under it:

# fdisk -l /dev/sdb

Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes, 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x00082e8c

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048  3907026943  1953512448   83  Linux

My fundamental question is this: Is there some advantage in creating a partition and then creating a filesystem on that partition, as compared to creating a filesystem on the whole disk and then mounting the whole disk ?

Answer 1

Is there any reason why a partition would be used in this case rather than a whole disk?

Few reasons I can think of:

• People (read: future admins) expect partition tables. Having them saves WTF moments. Filesystem on entire device may seem simpler – "I'm saving one abstraction layer, yay!" – but it's not one abstraction layer less, it's one possibility more.
• Programs may expect a partition table first, a filesystem later. See what can happen when things go wrong.

In my opinion the first reason alone is good enough. Additionally (these may not apply to your case though):

• In case you need to shrink the filesystem and create a multi-partition setup, it's easier when you already have a partition table.
• In case you need to place a bootloader somewhere, MBR with a single partition at some standard offset is a way better starting point than a filesystem on the entire device. I guess with GPT the problem converges to the point above.

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However if you need to move the disk back and forth between an enclosure that mangles its logical sector size and any setup that doesn't, a filesystem on the entire device would allow you to mount easier. Compare this question and my answer there.