How to get the number of physical disks in Linux?

Question

What is the command line command to get the number of physical disks in Linux Server and how much space is used on each?

Answer 1

sudo fdisk -l will list your disks and a bunch of stats about them, including the partitions. The disks are generally in the form of /dev/sdx and partitions /dev/sdxn, where x is a letter and n is a number (so sda is the first physical disk and sda1 is the first partition on that disk).

sudo df -h gives you the size and usage stats per partition. Drop the -h and you get usage in blocks, with it it's human readable.

I put the sudos in there because I got no output from fdisk and only partial output from df when I ran the commands as a regular user, I suppose because the commands read from somewhere off limits to non-admins.

Answer 2

You'd think there'd be a simple answer to this, but it actually depends on what you mean by "physical disk". iSCSI volumes and RAID devices (for example) appear as physical disks, but the tools one uses to examine these differ.

If you just mean a plain SATA or SCSI drive attached directly to a host controller on the motherboard of the server, you're looking for actively used devices located at /dev/sdN, so you can grep through your dmesg for them (dmesg | grep sd) or you could look in /dev/disk/by-id or yet again you can look in /proc/diskstats.

Once you've identified the /dev/ entry for devices that are present, you can use the appropriate tool to check for free space. This again depends on other info, such as how they were partitioned, whether they use the lvm, and so on.