Hypervisor
Hypervisor
Software that lets one physical server run multiple isolated virtual machines.
In everyday business: One powerful server can safely run several separate business servers.
STORAGE ARCHITECTURE
DAS, NAS, SAN, iSCSI and Fibre Channel Storage Playbook
Understand what the server actually sees, who owns the filesystem, how storage travels over the network and which design fits the workload.
Book 4 | Chapter 1
Chapter opening
Chapter 1 moves from the course overview into das, nas, san, iscsi and fibre channel storage. The aim is not to memorise product menus or commands. The reader should understand what problem the technology solves, how it fits into the wider storage technical textbook, what normal operation looks like, and how to prove the result in the field.
This is the first chapter in the sequence, so it establishes concepts that later chapters build on.
Learning objectives
- Explain the main purpose of DAS, NAS, SAN, iSCSI and Fibre Channel Storage in plain language.
- Distinguish capacity, performance, resilience and backup instead of treating them as the same requirement.
- Use evidence to separate a design problem from a configuration or physical fault.
- Describe the business impact of a failure and the evidence required for handover.
Why this matters in a real company
Storage is where company files, databases and virtual machines live. The business impact is not only capacity: performance, resilience, backup and recovery determine whether data remains usable when something fails.
Course: Storage Technical Textbook
PLAIN ENGLISH
Technical terms used in this chapter
You do not need to memorise the jargon first. Understand what each term does and why somebody running a company would care about it.
Throughput
Throughput
The amount of useful data moved in a period of time.
In everyday business: It helps describe how fast large backups, files or storage transfers can complete.
Latency
Latency
The delay before an operation or packet completes.
In everyday business: Users experience high latency as slowness even when headline bandwidth looks good.
Volume
Container Volume
Persistent storage kept separately from the short-lived container filesystem.
In everyday business: Company data can survive when an application container is replaced.
Backup
Backup
An independent recoverable copy of data or system state.
In everyday business: It is the safety net for deletion, corruption, ransomware, hardware loss or major mistakes.
iSCSI
Internet Small Computer Systems Interface
A protocol that carries block-storage commands over IP networks.
In everyday business: A server can use remote storage almost as if it were a local disk.
VLAN
Virtual LAN
A logical Layer 2 network that separates devices even when they use the same physical switches.
In everyday business: Staff, cameras and guest WiFi can be kept apart without buying a separate switch for each.
RAID
Redundant Array of Independent Disks
A method of combining drives for capacity, performance and/or tolerance of certain drive failures.
In everyday business: A failed disk does not always mean immediate data loss, but RAID is not a backup.
BUSINESS TRANSLATION
What this means outside the server room
This topic affects where company data lives, how fast applications respond and whether the business can continue after hardware or data problems.
RAID
What it means: RAID combines several drives so the storage system can keep operating through certain drive failures, depending on the RAID level.
In normal business language: Think of RAID as keeping the business open when one filing cabinet drawer breaks. It helps availability, but it does not protect you if somebody deletes the wrong folder, malware encrypts the files, or the whole building is lost.
Why the decision matters: Use RAID to reduce downtime from disk failure, and use backup for recovery from deletion, corruption, ransomware and larger disasters.
VLAN
What it means: A VLAN creates a separate logical network even when devices share the same physical switches.
In normal business language: Think of one office building with separate departments using the same corridors but different access-controlled areas. Staff, cameras, voice and guests can share the same switching hardware without all being in one open network.
Why the decision matters: Use VLANs to separate traffic for security, performance and easier troubleshooting without buying a separate physical switch for every department.
Hypervisor
What it means: A hypervisor lets one physical server run several isolated virtual machines.
In normal business language: Think of one office building divided into secure independent suites. The building is shared, but each tenant operates separately.
Why the decision matters: Virtualization reduces hardware sprawl and improves flexibility, but the physical host becomes important because several business systems can depend on it.
Virtual Machine
What it means: A virtual machine is a software-defined computer with its own operating system, memory, CPU allocation, disks and network interfaces.
In normal business language: It behaves like a separate server even though several VMs may share one physical machine.
Why the decision matters: VMs are useful for separating roles such as domain control, file sharing and applications while keeping management and recovery flexible.
Backup
What it means: A backup is an independent recoverable copy of data or system state.
In normal business language: Think of it as having a duplicate of important company records stored safely away from the live filing cabinet.
Why the decision matters: A backup only counts if it can be restored. Test recovery, not just backup completion.
NAT
What it means: NAT changes IP addresses as traffic crosses a network boundary.
In normal business language: It is similar to a company switchboard: many internal extensions can share one public number.
Why the decision matters: NAT helps with address use and publishing services, but it is not a substitute for firewall security.
Chapter contents
1.1 The storage secret that simplifies almost everything
Ask one question: who owns the filesystem? With NAS, the storage system owns the filesystem and clients access files or directories over protocols such as SMB or NFS. With block storage, the storage array presents blocks and the host normally creates the partition/filesystem or uses the block device for an application such as a hypervisor or database.
DAS
Direct-attached storage is connected directly to a host or controller. It can be simple and fast because there is no storage network in the path, but sharing and high availability depend on the host/storage architecture.
NAS
NAS is file storage. Clients access shares or exports. It is usually the natural choice for user files, departmental shares, general backup targets and workloads that expect file protocols. The storage system handles the underlying filesystem.
SAN
SAN is block storage presented to servers. Common transports include Fibre Channel and iSCSI. The server sees a LUN/block device rather than a remote file share. SANs are commonly used where hosts or hypervisors need shared block storage and where storage networking is managed deliberately.
iSCSI
iSCSI carries SCSI block commands over IP. The host runs an initiator and logs into a target. Red Hat documents discovery and login with iscsiadm, followed by the operating system seeing a SCSI disk device.
Linux initiator example
iscsiadm -m discovery -t sendtargets -p 192.0.2.60
iscsiadm -m node --login
Use the actual target IP, IQN, CHAP policy and multipath configuration supplied by the storage administrator.
Fibre Channel
Fibre Channel is a dedicated storage networking architecture using FC HBAs, switches and storage target ports. Zoning controls which initiators can communicate with which targets, while LUN masking on the storage side controls which logical units are presented to hosts. Do not confuse zoning with filesystem permissions.
Multipathing
A resilient block-storage design usually needs more than two cables. It needs independent usable paths that the host multipath software understands. Two NICs or HBAs cabled to the same failed switch are not two independent paths.
iSCSI network practices
- Use dedicated storage VLANs or networks where the design requires isolation and predictable operation.
- Keep MTU consistent end to end if jumbo frames are used. A partially configured jumbo-frame path creates hard-to-diagnose failures.
- Use multiple paths and multipath software rather than ordinary link aggregation when the storage design requires separate iSCSI paths.
- Verify NIC, switch and array port counters under load.
- Document target portals, IQNs, VLANs, initiators and LUN mappings.
What works and what does not
| Works | Does not work well |
|---|---|
| Choosing file vs block from application requirements. | Buying SAN because it sounds faster without checking workload and operational complexity. |
| Testing actual latency, IOPS and throughput. | Using interface line rate as the expected storage performance. |
| Independent storage paths with multipathing. | Calling two links redundant when they share the same failure point. |
| Consistent MTU when jumbo frames are used. | Changing MTU on only the server and storage. |
Client benefit
Choosing the correct storage architecture can simplify access, improve resilience and make expansion predictable. The wrong architecture can create unnecessary complexity even when the raw disks are fast.
RAID and Storage Performance | Storage Knowledge Centre | Storage at Server Warehouse | NAS Storage | SAN Storage
DEEPER TEACHING
DAS, NAS and SAN by filesystem ownership
Storage architecture becomes much easier when you first ask: who owns the filesystem? That single question separates many DAS, NAS and SAN designs.
DAS: direct attachment
Direct Attached Storage is connected directly to a server. The server sees the disks or logical volume and normally owns the filesystem. DAS is simple and can be fast, but sharing the same block device between multiple independent servers requires specific clustering/filesystem support.
NAS: ask for files
With NAS, the storage system owns the filesystem and clients ask for files or directories through a file protocol such as SMB or NFS. Permissions, snapshots and quotas are commonly managed at the NAS/file-service layer.
SAN: ask for blocks
A SAN presents block storage. The server sees a LUN as storage and creates or uses a filesystem/application structure on top of it. iSCSI transports SCSI commands over IP. Fibre Channel uses a dedicated FC fabric.
Worked selection example
| Requirement | Likely starting point | Reason |
|---|---|---|
| 30 staff sharing documents | NAS | Native multi-user file service |
| One standalone server with local database | DAS | Simple direct storage path |
| Several virtualization hosts needing shared block storage | SAN or supported shared platform | Hosts need centrally presented block storage and multipath design |
| Backup repository | NAS/DAS/object platform depending product | Driven by backup software, retention and recovery design |
Capacity is only one axis
A 40 TB system can be unsuitable for a 5 TB workload if its latency, IOPS, network path or recovery design is wrong. Storage design should record at least usable capacity, growth, workload type, performance expectations, failure tolerance, backup method and restore target.
Multipath reasoning
If a server has two iSCSI NICs but both connect through one physical switch, that switch remains a common failure point. True path redundancy requires independent failure domains and multipath software that understands multiple paths to the same LUN.
WORKED BUSINESS SCENARIO
Scenario: storage is online, but the business says it is slow
A storage system has free capacity and all disks show healthy, yet accounting reports are taking much longer and VM backups are overlapping into business hours.
What the chapter teaches us: Capacity and health LEDs do not prove performance. The investigation must separate application delay, host queues, network path, controller/cache behaviour and media performance.
Think it through
- Which measurements distinguish latency from throughput?
- Could the network be the bottleneck even when the array is healthy?
- What baseline would help prove whether the problem is new?
PRACTICAL WORK
Hands-on lab
Document a lab storage path from application to virtual or physical disk. Record usable capacity, RAID layout, network path if any, and backup destination.
Troubleshooting exercise
Storage is slow. Separate application, host queue, network, controller or cache and media metrics before replacing drives.
Chapter field checklist
- I can explain the subject without relying only on acronyms.
- I can draw or describe the main traffic, storage, power or service path.
- I know what normal operation should look like.
- I know which logs, counters or test results prove the result.
- I can explain the business impact if this component fails.
- I would document the final configuration and evidence at handover.
Chapter summary
DAS, NAS, SAN, iSCSI and Fibre Channel Storage Playbook should now be understood as a business service with a technical implementation, not simply a collection of commands or product names. The important habit is to know the purpose, understand the dependencies, measure the result and document what was proven.
END OF CHAPTER
Review questions
- Explain the subject in plain language to a business owner.
- List the main dependencies that must be healthy before this service can work.
- Describe one realistic failure and the first three pieces of evidence you would collect.
- Explain what should be documented at handover.
- Why are RAID and backup different controls?
- How do latency, IOPS and throughput describe different aspects of storage performance?
A good answer should explain the reason, not only repeat a product name or command.
Technical references
Use the current project specification and exact manufacturer documentation for the installed products. These references support the technical principles explained here.