Disk Concept -Boot Disk and Persistent Disk
Google Cloud — Easy Study Notes
Essential Google Cloud Infrastructure: Foundation
1. What is Google Cloud?
Google Cloud is basically a collection of computing, storage, networking, database, security and other IT services provided by Google.
Instead of buying physical servers yourself, you can rent/use Google's infrastructure.
Simple example
Traditional company:
Company
↓
Buy physical servers
↓
Install OS
↓
Configure network
↓
Maintain hardware
↓
Run application
Google Cloud:
You
↓
Choose Google Cloud service
↓
Configure it
↓
Run your application
Google manages the underlying physical infrastructure.
2. Cloud Computing — Basic Idea
Cloud computing means:
Using computing resources over the internet instead of owning all the physical hardware yourself.
You can get:
CPU
RAM
Storage
Network
Databases
Kubernetes
Application platforms
Security services
when you need them.
3. Google Cloud Projects
A Project is one of the most important concepts in Google Cloud.
Think of a project as a container/folder for your cloud resources.
Google Cloud
│
├── Project A
│ ├── VM
│ ├── Storage
│ └── Network
│
└── Project B
├── VM
├── Database
└── Network
Resources are created inside projects.
Why projects?
Projects help with:
Organizing resources
Separating environments
Access control
Billing
Resource management
Example:
Company
│
├── Development Project
├── Testing Project
└── Production Project
4. Projects and Billing
A project can be associated with a billing account.
Think:
Project
↓
Uses cloud resources
↓
Creates usage/cost
↓
Billing account pays
So:
Project = organizes resources
Billing account = pays for usage
5. Ways to Work with Google Cloud
There are three major ways to interact with Google Cloud.
1. Google Cloud Console
A web-based graphical interface.
Browser
↓
Google Cloud Console
↓
Click buttons / configure services
Good for beginners and visual management.
2. Cloud Shell
A command-line environment available from Google Cloud.
Example:
gcloud compute instances list
You type commands instead of clicking.
Cloud Shell is useful for learning and automation.
3. APIs
Applications can communicate directly with Google Cloud services.
Your application
↓
Google Cloud API
↓
Cloud service
Useful when software needs to automate cloud operations.
Easy memory
Console → Click
Cloud Shell → Command
API → Program
6. Google Cloud Marketplace
Marketplace provides ready-made software/application solutions.
Instead of manually installing every component, you can deploy a preconfigured solution.
Example: LAMP
LAMP means:
L → Linux
A → Apache
M → MySQL
P → PHP
Marketplace can deploy this kind of environment for you.
After deployment, you can access/manage the application using the provided site URL.
7. Compute Options in Google Cloud
Google Cloud gives you different levels of control.
Think of this as:
More control
↑
Compute Engine
│
GKE
│
Cloud Run
│
Serverless functions
↓
Less infrastructure management
8. Compute Engine
Compute Engine = Virtual Machines (VMs).
A VM is basically a computer running inside Google's data center.
Think:
"Google gives me a computer, and I control the computer."
You can choose:
Operating system
CPU
RAM
Disk
Network
Software
Security settings
Compute Engine gives you a lot of flexibility.
This is called:
Infrastructure as a Service (IaaS)
9. What is a VM?
VM = Virtual Machine
Think of a physical computer:
Computer
│
├── CPU
├── RAM
├── Disk
├── Network
└── Operating System
A Google Cloud VM provides the same basic concepts virtually.
Google Cloud VM
│
├── Virtual CPU
├── RAM
├── Disk
├── Network
└── Operating System
10. Creating a VM — The 4 Things to Remember
When creating a VM, think about:
1. WHERE?
2. HOW POWERFUL?
3. WHICH OS?
4. HOW CONNECTED?
1. Where?
Choose:
Region + Zone
2. How powerful?
Choose:
Machine type
CPU + RAM
3. Which OS?
Choose:
Boot disk / OS image
Example:
Linux
Windows
4. How connected?
Choose:
Network / VPC / firewall configuration
11. Region and Zone
Region
A region is a geographical area containing Google Cloud infrastructure.
Examples:
us-central1
europe-west1
asia-south1
Zone
A zone is a smaller location inside a region.
Example:
Region: asia-south1
├── Zone A
├── Zone B
└── Zone C
A VM is normally created in a zone.
Easy memory
Region = bigger area
Zone = smaller location inside region
12. Machine Type
Machine type determines how much computing power your VM gets.
Main things to think about:
Machine Type
│
├── CPU
└── Memory (RAM)
For example:
e2-medium
├── 2 vCPU
└── 4 GB memory
Different machine families are designed for different workloads.
13. CPU and Memory
CPU
CPU performs calculations and executes instructions.
Think:
CPU = worker
More CPU → more processing capability.
Memory / RAM
RAM is temporary working space.
Think:
RAM = worker's desk
A worker with a bigger desk can keep more things available while working.
Simple analogy
CPU = Worker
RAM = Desk
Disk = Cupboard
CPU works on things.
RAM holds things currently being worked on.
Disk stores things for longer.
14. Machine Family Concepts
Google Cloud provides different machine types for different needs.
Common categories include:
General purpose
Balanced CPU and memory.
Good for normal applications.
High-CPU / compute-focused
More CPU relative to memory.
Good for CPU-heavy workloads.
High-memory
More RAM.
Good for memory-intensive applications.
Memory-optimized
Designed for workloads requiring very large amounts of memory.
Compute-optimized
Designed for demanding CPU workloads.
Shared-core
Smaller machines where CPU resources are shared.
15. Boot Disk vs Persistent Disk — IMPORTANT
This was the confusing part, so remember it this way:
"Boot" describes the PURPOSE
Boot disk = disk used to start the VM.
It contains the operating system.
VM starts
↓
Boot Disk
↓
Linux / Windows
↓
Operating System loads
↓
VM starts working
"Persistent" describes the BEHAVIOR
Persistent disk = storage that remains available independently of the VM's compute lifecycle.
So these are NOT opposites.
A disk can be:
Boot + Persistent
16. Very Simple Disk Example
Imagine your laptop.
The laptop has an SSD.
That SSD can contain:
Windows
Applications
Photos
Documents
The same idea applies to a VM.
VM
│
└── Boot Persistent Disk
│
├── Linux
├── Applications
└── Files
So:
Boot = what the disk is used for
Persistent = how the disk behaves
17. Can We Separate OS and Data?
Yes.
Option 1 — Same disk
Boot Persistent Disk
│
├── Linux
├── Applications
└── Data
Simple setup.
Option 2 — Separate disks
VM
│
├── Boot Persistent Disk
│ └── Linux / OS
│
└── Additional Persistent Disk
└── Database / Application data
Both are possible.
18. Persistent Disk
Persistent Disk is network-attached storage.
It is separate from the VM's CPU and RAM.
VM
│
├── CPU
├── RAM
└────── network ──────→ Persistent Disk
Because the disk is separate from compute, the disk can survive independently.
Important features
Persistent disks can:
Survive VM restart
Remain after VM deletion if configured correctly
Be resized
Be snapshotted
Be attached to VMs
Be used for boot or data storage
19. Delete Boot Disk When Instance Is Deleted
When creating a VM, there is an option:
Delete boot disk when instance is deleted
If enabled:
Delete VM
↓
Boot disk deleted
If disabled:
Delete VM
↓
Boot disk remains
This is important when you want to preserve the disk/data.
20. Persistent Disk Types
There are different performance/cost options.
Standard Persistent Disk
Uses HDD technology.
Good for:
Large capacity
Lower cost
Sequential I/O
Workloads where very high performance isn't required
Think:
Cheap + capacity
Balanced Persistent Disk
Uses SSD.
Balances:
Cost ↔ Performance
Good general-purpose option.
Think:
Normal applications
SSD Persistent Disk
Uses SSD.
Good for:
High-performance applications
Databases
Lower latency
Higher IOPS
Think:
Performance
Extreme Persistent Disk
Designed for very demanding workloads.
Good for:
High-end databases
Very high IOPS
Random-access workloads
High throughput
You can provision desired IOPS.
Think:
Maximum persistent-disk performance
21. Zonal vs Regional Persistent Disk
Zonal Persistent Disk
Associated with one zone.
Region
│
└── Zone A
└── Persistent Disk
Regional Persistent Disk
Data is synchronously replicated across two zones in the same region.
Region
│
├── Zone A → Disk replica
│
└── Zone B → Disk replica
Useful when you need higher availability.
Easy memory
Zonal = one zone
Regional = two zones
22. Disk Snapshots
A snapshot is a point-in-time backup of a persistent disk.
Persistent Disk
↓
Snapshot
↓
Backup / Recovery
Snapshots are incremental, so later snapshots can store changes rather than making a completely independent full copy each time.
23. Persistent Disk Can Be Resized
One useful feature is that persistent disks can be expanded.
Example:
100 GB
↓
200 GB
You don't have to replace the physical disk.
The disk and underlying infrastructure are managed by Google Cloud.
24. Read-Only Persistent Disk
A persistent disk can be attached in read-only mode to multiple VMs.
Disk
│
┌──────┼──────┐
↓ ↓ ↓
VM1 VM2 VM3
READ READ READ
Useful when multiple VMs need the same static data.
25. Disk Encryption
Google Cloud encrypts data at rest by default.
You don't have to manually encrypt every file yourself.
You can also have more control using encryption keys.
Google-managed
Google manages the encryption.
Customer-managed encryption keys
You manage keys using Cloud KMS.
Customer-supplied encryption keys
You supply/manage the keys yourself.
Easy memory
Default → Google manages encryption
More control → You manage keys
26. Local SSD
Local SSD is different from Persistent Disk.
Local SSD is physically associated with the VM's host infrastructure.
It provides very high performance.
VM
│
├── CPU
├── RAM
└── Local SSD
↓
Very fast
But it is ephemeral.
That means:
Don't use it as the only place for important permanent data.
The course notes that Local SSD data survives a VM reset, but not a VM stop/terminate.
27. RAM Disk
A RAM disk stores data in memory.
Linux can use tmpfs.
Application
↓
RAM
↓
Very fast
RAM disk is extremely fast but volatile.
If the memory is lost, the data is lost.
Good for:
Temporary data
Cache
Small data structures
Very performance-sensitive temporary workloads
28. Storage Performance vs Durability
Remember this simple order:
Durability
Persistent Disk
↓
Local SSD
↓
RAM Disk
Speed
Persistent Disk
↓
Local SSD
↓
RAM Disk
↑
FASTEST
The basic idea:
Persistent Disk → durable
Local SSD → very fast but temporary
RAM Disk → fastest but extremely temporary
29. Number of Disks
The number of persistent disks that can be attached depends on the machine type.
From the course:
Shared-core
→ up to 16 disks
Many larger machine categories
→ up to 128 disks
So one VM can have a large amount of attached storage.
30. Disk I/O and Network Bandwidth
This is an important performance concept.
Disk I/O and network traffic can compete for available bandwidth.
VM
│
┌──────┴──────┐
↓ ↓
Disk I/O Network I/O
│ │
└──────┬──────┘
↓
Shared resources
So adding lots of disks doesn't automatically mean unlimited throughput.
If your VM is doing:
Heavy disk operations
Large network transfers
both can consume bandwidth.
31. Physical Disk vs Cloud Persistent Disk
Traditional physical computer:
Physical Disk
↓
Partition
↓
Filesystem
↓
OS/Data
You may need to manually handle:
Partitioning
Resizing
Redundancy
Encryption
Backups
Google Cloud Persistent Disk abstracts much of this complexity.
You can:
Resize disks
Snapshot disks
Use built-in redundancy
Use encryption
Use customer-managed keys
Think:
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