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Understanding Your Disk Stack: From RAID Controller to LVM Logical Volume

When you run sudo fdisk -l or lsblk on a Linux server, you may encounter device names and disk models that look unfamiliar. This post walks through a real-world example to explain what each layer means — from the hardware RAID controller all the way up to an LVM logical volume.

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Step 1: Reading the fdisk Output

sudo fdisk /dev/sda

Disk /dev/sda: 13.97 TiB, 15358534615040 bytes, 29997137920 sectors
Disk model: MR9460-16i
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 262144 bytes / 1048576 bytes
Disklabel type: gpt
Disk identifier: 723D7EC3-6663-42B3-B099-4EFD50D34116

Device       Start         End     Sectors Size Type
/dev/sda1     2048     2203647     2201600   1G EFI System
/dev/sda2  2203648     6397951     4194304   2G Linux filesystem
/dev/sda3  6397952 29997135871 29990737920  14T Linux filesystem

The Disk model field shows MR9460-16i. This is not the brand name — it is the model number of a Broadcom (LSI) MegaRAID SAS 9460-16i hardware RAID controller.

Field	Value
Brand	Broadcom / LSI
Product line	MegaRAID SAS
Model	9460-16i
Internal ports	16
Bus	PCIe

The key takeaway: /dev/sda is not a single physical disk. It is a virtual drive (logical drive) exposed by the RAID controller to the operating system. Behind the scenes, the controller manages multiple physical disks assembled into a RAID array totaling ~14 TB.

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Step 2: Partition Layout

The three partitions follow a standard Ubuntu server layout:

Device	Size	Type	Purpose
/dev/sda1	1 G	EFI System	UEFI boot partition
/dev/sda2	2 G	Linux filesystem	/boot
/dev/sda3	~14 T	Linux filesystem	LVM Physical Volume

/dev/sda3 occupies almost all of the available space and serves as the base for LVM.

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Step 3: What Is /dev/mapper/ubuntu–vg-lv–1?

After partitioning, the Ubuntu installer sets up LVM (Logical Volume Manager) on top of /dev/sda3. LVM adds a flexible abstraction layer between physical partitions and mounted filesystems.

The device /dev/mapper/ubuntu--vg-lv--1 is an LVM logical volume created by the Ubuntu installer.

Decoding the Name

/dev/mapper/ubuntu--vg-lv--1
                │        │
                │        └── Logical Volume (LV) name: lv-1
                └── Volume Group (VG) name: ubuntu-vg

Note: LVM replaces each - in names with -- inside the /dev/mapper/ path to avoid ambiguity.

Full Stack Diagram

Physical Disks (managed by RAID controller)
  └── /dev/sda              ← Virtual drive exposed by MegaRAID 9460-16i
        ├── /dev/sda1       ← EFI System partition
        ├── /dev/sda2       ← /boot
        └── /dev/sda3       ← LVM Physical Volume (PV)
              └── ubuntu-vg ← LVM Volume Group (VG)
                    └── lv-1 ← LVM Logical Volume (LV)
                          └── /dev/mapper/ubuntu--vg-lv--1  ← mounted as /

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Step 4: Useful Commands

Inspect the RAID controller and physical disks:

# Using storcli (Broadcom's CLI tool)
storcli64 /c0 show
storcli64 /c0/eall/sall show

# Using legacy megacli
megacli -PDList -aALL

Inspect the LVM stack:

pvdisplay          # Physical volumes
vgdisplay          # Volume groups
lvdisplay          # Logical volumes
lsblk              # Full block device tree

Expected lsblk output:

NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                         8:0    0 13.97T  0 disk
├─sda1                      8:1    0    1G   0 part /boot/efi
├─sda2                      8:2    0    2G   0 part /boot
└─sda3                      8:3    0   14T   0 part
  └─ubuntu--vg-lv--1      253:0    0   14T   0 lvm  /

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Summary

Layer	Technology	Device
Hardware	MegaRAID 9460-16i RAID controller	physical disks
Block device	RAID virtual drive	/dev/sda
Partitioning	GPT	/dev/sda1~3
Volume management	LVM	/dev/mapper/ubuntu--vg-lv--1
Filesystem	ext4 / xfs	mounted at /

Understanding this stack is essential when planning disk expansions, replacing failed drives, resizing logical volumes, or diagnosing I/O performance issues on Linux servers.

Notes

Windows Disk management: diskpart, diskmgmt.msc