Disk Attachment

Means how secondary storage devices are connected to a computer system.

Host-attached

Storage device directly connected to the host. Connection uses one or more I/O buses. Controlled by the host’s OS.

The I/O bus could be:

• ATA (Advanced Technology Attachment)
• SATA (Serial ATA)
• eSATA
• SCSI
• SAS (Serial Attached SCSI)
• NVMe (NVM express)
• USB (Universal Serial Bus)
• FC (Fibre Channel)

SATA

Most common one.

NVMe

Faster interface than SATA. Designed for NVM. Connects directly to PCI bus.

Fibre Channel

High speed serial architecture using fibre or copper cables. Multiple hosts and

Used in high-end systems.

Network-attached

Disk is connected to multiple systems through a local network. Uses high-speed networks and standard network protocols. Allows file-level access. Implemented via remote procedure calls (RPCs) over TCP or UDP. Mounted as a disk. A self-contained device with its own filesystem and OS.

Commonly used protocols:

• NFS (Network File System)
• CIFS (Common Internet File System)

Uses network bandwidth and adds latency.

Used in servers, cloud storage, and large data centers.

Cloud Storage

Storage is placed on a remote data center. Connected through internet. Access is done through an API.

Examples: S3, OneDrive.

Storage Array

Aka. disk array or SAN array. A specialized hardware system that combines many disks into a single logical storage. Allows block-level reads/writes. Designed for high performance, reliability, and scalability in enterprise data centers.

The storage array controller provides:

• Ports to connect hosts to array
• Memory, controlling software
• Common features found in file systems

The Storage Area Network (SAN) controller (aka. storage array controller) manages RAID, caching.

Storage Area Network

A network of storage arrays. Connected using Fibre Channel or InfiniBand switches. Hosts connect to the same switches, to access the storage arrays. Connected servers format the physical blocks with their own filesystems.

Uses protcols like

• Fibre Channel
• iSCSI (Internet Small Computer Systems Interface): Uses IP network to carry SCSI commands.
• NVMe-oF

Compared to NAS:

• Lower latency
• High throughput
• High scalability

Avoids bandwidth congestion which is a limiation of NAS.

InifiniBand

Has high speed and low latency compared to Fibre Channel or Ethernet.

LUN Masking

A security and access-control feature used in SAN. Ensures that only specific hosts can access specific LUNs (Logical Unit Numbers), which are virtual disks presented by a storage array.

Each server in the SAN has a unique identifier world wide name (WWN). The storage array maps or masks LUNs so only approved WWNs can see and use them. Other servers cannot detect or access those LUNs, preventing accidental overwrite or data leaks.