Tag: Namespace

In the world of SCSI, a storage device is generally addressed by two things:

1. LUN–Logical Unit Number. This is a number used to address the device down a specific path to a specific array, for a specific host. So it is not a unique number really, it is not guaranteed to be unique to an array, to a host, or a volume. So for every path to a volume there could be a different LUN number. Think of it like a street address. 100 Maple St. There are many “100 Maple Streets”. So it requires the city, the state/province/etc, the country to really be meaningful. And a street name can change. So can other things. So it can usually get you want you want, but it isn’t guaranteed.
2. Serial number. This is a globally unique identifier of the volume. This means it is entirely unique for that volume and it cannot be change. It is the same for everyone and everything who uses that volume. To continue our metaphor, look at it like the GPS coordinates of the house instead of the address. It will get you where you need, always.

So how does this change with NVMe? Well these things still exist, but how they interact is…different.

Now, first, let me remind that generally these concepts are vendor neutral, but how things are generated, reported, and even sometimes named vary. So I write this for Pure Storage, so keep that in mind.