Disaster Recovery

Disaster Recovery: Your Digital Safety Net

The Story of the Backup Kingdom

Imagine you have a treasure chest full of your favorite toys. One day, a storm comes and floods your room. All your toys are ruined! But wait—your smart mom kept copies of your favorite toys in grandma’s house across town. Within a day, you’re playing again!

That’s Disaster Recovery in a nutshell. It’s your plan to get back on your feet when bad things happen to your computer systems.

Recovery Objectives: RTO & RPO

The Two Magic Numbers

Think of running a lemonade stand. You keep track of every cup you sell in a notebook.

RPO (Recovery Point Objective) = How much notebook writing can you afford to lose?

• If you only copy your notebook once a day, and a dog eats it at 3 PM, you lose everything since morning
• RPO answers: “How old can my backup be?”

RTO (Recovery Time Objective) = How fast do you need to reopen your lemonade stand?

• If customers can only wait 1 hour, your RTO is 1 hour
• RTO answers: “How long can I be closed?”

graph TD
    A["Disaster Strikes!"] --> B{Two Questions}
    B --> C["RPO: How much data can we lose?"]
    B --> D["RTO: How long can we be down?"]
    C --> E["Backup Frequency"]
    D --> F["Recovery Speed"]

Real Examples

Simple Rule:

• Lower RPO = More frequent backups = More expensive
• Lower RTO = Faster recovery = More expensive

Disaster Recovery Strategies

The Four Rescue Plans

Imagine you have a house. How do you prepare for a fire?

1. Backup & Restore (The Storage Unit)

What it is: Keep copies in a storage unit. If your house burns, buy new furniture and move your stuff back.

How it works:

• Save your data to storage regularly
• If disaster happens, set up new computers
• Load your saved data onto them

Best for: Small businesses, non-critical apps Recovery time: Hours to days Cost: Cheapest option

2. Pilot Light (The Tiny Flame)

What it is: Like keeping a small pilot light burning on your stove. The core is always warm, ready to fire up.

How it works:

• Keep your database running (small and cheap)
• Other servers are OFF
• When disaster strikes, turn everything ON

Best for: Medium businesses Recovery time: Minutes to hours Cost: Low to moderate

3. Warm Standby (The Ready Room)

What it is: A smaller version of your house, always furnished and ready. Just need to move in.

How it works:

• Run a smaller copy of everything
• Data syncs regularly
• Scale up when needed

Best for: Important business apps Recovery time: Minutes Cost: Moderate

4. Hot Standby / Active-Active (The Twin Houses)

What it is: Two identical houses. People live in both. If one burns, everyone just uses the other.

How it works:

• Run TWO complete systems
• Both handle real traffic
• If one fails, the other continues instantly

Best for: Critical systems (banks, hospitals) Recovery time: Seconds Cost: Most expensive

graph TD
    A["DR Strategies"] --> B["Backup & Restore"]
    A --> C["Pilot Light"]
    A --> D["Warm Standby"]
    A --> E["Hot Standby"]
    B --> F["Hours-Days"]
    C --> G["Mins-Hours"]
    D --> H["Minutes"]
    E --> I["Seconds"]

Backup Strategies

The Three Backup Friends

Meet your three backup helpers!

1. Full Backup (The Complete Copy)

What it is: Copy EVERYTHING. Every single file. Every time.

Like: Photocopying your entire notebook every day

Pros:

• Easy to restore (just one copy needed)
• Simple to understand

Cons:

• Takes long time
• Uses lots of storage
• Expensive

When to use: Weekly or monthly

2. Incremental Backup (The Daily Diary)

What it is: Only copy what CHANGED since the LAST backup (any type).

Like: Only writing down what’s NEW in your diary each day

Pros:

• Very fast
• Uses little storage

Cons:

• To restore, need ALL incrementals in order
• Like a chain—if one link breaks, trouble!

When to use: Daily or hourly

3. Differential Backup (The Weekly Summary)

What it is: Copy everything that changed since the LAST FULL backup.

Like: Keeping a running list of changes since Sunday

Pros:

• Faster restore than incremental
• Only need full backup + latest differential

Cons:

• Gets bigger each day
• More storage than incremental

When to use: Daily

Backup Schedule Example

The 3-2-1 Rule:

• 3 copies of your data
• On 2 different types of storage
• With 1 copy offsite (different location)

Cross-Region Replication

Spreading Your Eggs

Your grandma always said: “Don’t put all your eggs in one basket!”

Cross-region replication means keeping copies of your data in different geographical locations.

Why Different Regions?

Imagine all your toy backups are in your house. What if:

• An earthquake hits your whole city?
• The power goes out in your entire state?
• A flood covers your whole region?

Solution: Keep copies in different cities, countries, or even continents!

How It Works

graph TD
    A["Your Main Data<br>New York"] --> B["Copy 1<br>California"]
    A --> C["Copy 2<br>London"]
    A --> D["Copy 3<br>Tokyo"]
    B --> E["If NY fails,<br>use CA!"]
    C --> F["If US fails,<br>use London!"]

Replication Types

Synchronous (Real-time Twin):

• Data saved to ALL locations at the same time
• Like sending the same text to all your friends instantly
• Zero data loss, but slower

Asynchronous (Delayed Copy):

• Data copied with a small delay
• Like forwarding an email a few seconds later
• Faster, but might lose a few seconds of data

Real Example

Disaster Recovery Testing

Practice Makes Perfect!

Would you trust a firefighter who never practiced putting out fires? Of course not!

DR testing = Practicing your recovery plan before a real disaster happens.

Types of DR Tests

1. Walkthrough Test (The Story Time)

What: Team sits together and talks through the plan step by step.

Like: Reading a fire escape plan with your family

Finds: Missing steps, unclear instructions

2. Tabletop Exercise (The Board Game)

What: Team pretends a disaster happened and discusses responses.

Like: Playing a “what if” game

Example scenario: “It’s Monday 9 AM. The main database just crashed. What do we do?”

3. Simulation Test (The Fire Drill)

What: Actually perform recovery steps, but don’t switch real traffic.

Like: Practicing your school fire drill

Finds: Technical problems, timing issues

4. Full Interruption Test (The Real Deal)

What: Actually fail over to backup systems with real traffic.

Like: Actually evacuating during a drill

Finds: Everything! But risky and expensive.

Testing Schedule

Golden Rules:

• Test regularly (untested plans are just wishes!)
• Document everything
• Fix problems you find
• Test again after changes

Data Synchronization

Keeping Everyone on the Same Page

Imagine you and your friend both have the same sticker collection list. When you add a new sticker, how do you make sure your friend’s list matches yours?

Data synchronization = Keeping multiple copies of data identical.

Sync Methods

1. One-Way Sync (The Loudspeaker)

How: Data flows from source to destination only.

Like: A teacher announcing to students (students don’t talk back)

Use case: Sending backups to storage

graph LR
    A["Main Server"] --> B["Backup Server"]
    A --> C["Another Backup"]

2. Two-Way Sync (The Phone Call)

How: Changes flow in both directions.

Like: Two friends updating each other

Use case: Multiple active sites

graph LR
    A["Server A"] <--> B["Server B"]

Sync Timing

Real-time Sync:

• Changes copied instantly
• Like texting—message arrives immediately
• Best for: Critical data (bank transactions)

Scheduled Sync:

• Changes copied at set times
• Like checking mailbox once a day
• Best for: Large files, non-urgent data

Batch Sync:

• Changes collected, then sent together
• Like saving up letters and mailing once a week
• Best for: Analytics, reports

Handling Conflicts

What if two people change the same thing at the same time?

Last Write Wins:

• Most recent change keeps
• Simple but might lose data

Version Tracking:

• Keep all versions
• User decides which to keep

Merge:

• Combine both changes if possible
• Smart but complex

Sync Health Checks

Putting It All Together

Your DR Recipe

1. Know your numbers: Set RPO and RTO
2. Choose your strategy: Based on budget and needs
3. Plan your backups: Full + Incremental/Differential
4. Spread your data: Cross-region replication
5. Test regularly: Don’t skip this!
6. Keep in sync: Monitor your data copies

Quick Decision Guide

graph TD
    A["How critical is your data?"] --> B{Can you lose data?}
    B -->|No way!| C["RPO: 0, Use Hot Standby"]
    B -->|A little OK| D{How long can you be down?}
    D -->|Seconds| E["Use Active-Active"]
    D -->|Minutes| F["Use Warm Standby"]
    D -->|Hours| G["Use Pilot Light"]
    D -->|A day| H["Use Backup & Restore"]

Remember This!

Disaster Recovery is like insurance:

• You hope you never need it
• But when you do, you’re SO glad you have it!

The best DR plan is one that’s:

• Written down
• Tested regularly
• Updated when things change
• Understood by the whole team

Now you’re ready to protect your digital treasures!