Why the output of lsblk have almost the same lines?

Question

lsblk -d -o NAME,SIZE,TYPE | grep disk

show me the such things

sda  894.3G disk
sdb  894.3G disk
sdc    3.7T disk
sdd    3.7T disk
nbd0    64G disk

Are the sda and sdc have sdb and sdd similarly physical devices? Either they're "physical" and "logical" devices?

It's not my own server, so I cannot see its specifications. The server was deployed without my participation.

Answer 1

Yes, those are 5 separate disks. You have 4 disks connected via the SCSI interface (sda, sdb, sdc and sdd). You also have one network block device, a physical disk on a remote machine that has been made available to your machine over NBD.

This is quite a normal setup (apart from the NBD which isn't very common these days). You very often have similar disks on a server since the server's administrator would have bought a few together and since having disks of the same size makes setting up RAID systems is much simpler. It isn't strange or surprising.

You can investigate further using parted -l which will will show the model and make of the disks. Or you can use more general commands for hardware information like lshw or hwinfo.

Answer 2

I've used hdparm util and check info about sda and sdb disks. They're disks of one model, but every of them have separate Serial Number. So they're separate but similar physical devices.