Why make a partition at all for mdadm/raid?

Question

i have 4 disks, sd[a,b,f,g] of various sizes that I want to 'merge' together. I am using mdadm to achieve this.

my question is, what's the difference between --

mdadm --create /dev/md0 --level=linear --raid-devices=4 /dev/sda /dev/sdb /dev/sdf /dev/sdg

and

mdadm --create /dev/md0 --level=linear --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdf1 /dev/sdg1

When both work? For some reason (if someone could explain this too, it would be awesome) I lose a lot of disk space as is when I look at /dev/md0 but if I create partitions and then create a linear raid, I end up losing even more space.

So why create partitions at all? Even when I do not have this setup and just want to use a disk, can I just do a mkfs.ext3 /dev/sda ?

---

Additional stuff - Here's /proc/partitions -

8 0 244140625 sda
8 1 244139008 sda1
8 16 244140625 sdb
8 17 244139008 sdb1
8 80 39063024 sdf
8 81 39061504 sdf1
8 96 156290904 sdg
8 97 156289024 sdg1

WHy are the sizes of my partitions smaller than my disk as listed above?

Answer 1

Why make a partition at all

You need partitions if you want to use part of a drive for RAID for a specific array. You can also be more flexible with more partitions.

Example:

1 TB HDD #1:    SDA1 (500 MB)     SDA2 (490 MB)
1 TB HDD #2:    SDB1 (500 MB)     SDB2 (490 MB)
1 TB HDD #3:    SDC1 (500 MB)     SDC2 (500 MB)

I can add sda1, sdb1 and sdc1 in a stripe for performance,
and sda2 and sdb2 in a mirror for security,
amd sdc2 just as a plain disk.

I can not do that if I use the whole drive.

In your case you seem to want only one single large setup, which means that it does not matter which way you do it.