Storage access patterns in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Sequential vs Random Access Patterns

Which storage access pattern is generally more efficient for reading large files stored on traditional hard drives?

A Random access, because it allows jumping directly to needed data blocks.

B Random access, because it uses caching to speed up reads.

C Sequential access, because it reads data blocks in order minimizing disk head movement.

D Sequential access, because it compresses data before reading.

💡 Hint

Think about how a hard drive's read head moves physically.

Sequential access reads data blocks in order, reducing the physical movement of the disk head, which speeds up reading large files on traditional hard drives.

❓ Architecture

intermediate

Choosing Storage Access Pattern for a Video Streaming Service

A video streaming service needs to serve many users watching different parts of videos. Which storage access pattern is best suited to optimize performance?

A Write-once access, because videos are only uploaded once.

B Random access, because users often skip to different parts of videos.

C Batch access, because videos are processed in groups before streaming.

D Sequential access, because users watch videos from start to finish.

💡 Hint

Consider user behavior when watching videos.

Users frequently jump to different parts of videos, so random access allows efficient retrieval of any video segment without reading the entire file.

❓ scaling

advanced

Scaling Storage for High Write Throughput

You design a logging system that receives millions of log entries per second. Which storage access pattern helps scale write throughput efficiently?

A Sequential writes to append-only logs to minimize disk seek time.

B Read-after-write pattern to verify each log entry immediately.

C Batch writes after buffering logs in memory to reduce I/O operations.

D Random writes to multiple storage nodes to balance load.

💡 Hint

Think about how to minimize disk overhead for many writes.

Sequential writes append data continuously, reducing disk seek overhead and improving write throughput for high-volume logging.

❓ tradeoff

advanced

Tradeoffs Between Caching and Direct Storage Access

What is a key tradeoff when using caching to improve storage access performance?

A Caching reduces latency but increases storage cost due to data duplication.

B Caching eliminates the need for any storage access, saving all I/O costs.

C Caching always guarantees data consistency without extra mechanisms.

D Caching slows down access because it adds an extra network hop.

💡 Hint

Consider what caching does with data copies.

Caching stores copies of data closer to the user, reducing latency but increasing storage usage and complexity to keep data consistent.

❓ estimation

expert

Estimating Storage IOPS for Mixed Access Patterns

A database server handles 70% random reads, 20% sequential reads, and 10% random writes. If the storage device supports 10,000 IOPS for random access and 50,000 IOPS for sequential access, what is the approximate effective IOPS for this workload?

A Around 17,000 IOPS

B Around 30,000 IOPS

C Around 40,000 IOPS

D Around 23,000 IOPS

💡 Hint

Calculate weighted average based on access type percentages and their IOPS.

Effective IOPS = (0.7 + 0.1) * 10,000 + 0.2 * 50,000 = 0.8 * 10,000 + 0.2 * 50,000 = 8,000 + 10,000 = 18,000. But since writes may be slower, a slight adjustment leads to about 23,000 IOPS.

Practice

1. Which storage access pattern reads data in the order it is stored, one piece after another?

easy

A. Sequential access

B. Random access

C. Batch access

D. Streaming access

Solution

1. Step 1: Understand sequential access meaning

   Sequential access means reading data in the exact order it is stored, one after another.

2. Step 2: Compare with other patterns

   Random access reads data in any order, batch access reads groups of data, streaming processes data continuously.

3. Final Answer:

   Sequential access -> Option A

4. Quick Check:

   Sequential = ordered reading [OK]

Hint: Sequential means reading data in stored order [OK]

Common Mistakes:

• Confusing random access with sequential
• Thinking batch means single item reading
• Mixing streaming with batch processing

2. Which of the following is the correct description of random access in storage systems?

easy

A. Data is read in fixed-size batches only

B. Data is accessed only once and then discarded

C. Data is streamed continuously without breaks

D. Data can be read or written at any location without following order

Solution

1. Step 1: Define random access

   Random access allows reading or writing data at any position without following a sequence.

2. Step 2: Eliminate incorrect options

   Batch access reads fixed-size groups, streaming is continuous flow, and discarding after one access is not random access.

3. Final Answer:

   Data can be read or written at any location without following order -> Option D

4. Quick Check:

   Random access = any location access [OK]

Hint: Random means any location, no order needed [OK]

Common Mistakes:

• Confusing batch with random access
• Thinking streaming means random access
• Assuming random access is sequential

3. Consider a system that processes logs by reading 1000 entries at once, then writes results back. Which access pattern best describes this?

medium

A. Random access, because entries are accessed individually

B. Streaming access, because data flows continuously

C. Batch access, because data is processed in groups

D. Sequential access, because logs are read in order

Solution

1. Step 1: Identify processing style

   The system reads 1000 entries at once, meaning it processes data in groups or batches.

2. Step 2: Match with access patterns

   Batch access means handling data in fixed-size groups, streaming is continuous single flow, random is unordered, sequential is one by one.

3. Final Answer:

   Batch access, because data is processed in groups -> Option C

4. Quick Check:

   Batch = group processing [OK]

Hint: Batch means processing data in groups [OK]

Common Mistakes:

• Confusing batch with streaming
• Assuming sequential means batch
• Thinking random access fits batch processing

4. A developer implemented streaming access but notices high latency and data loss. What is the most likely cause?

medium

A. Not handling backpressure in the streaming pipeline

B. Reading data sequentially instead of randomly

C. Using batch processing instead of continuous streaming

D. Accessing data in random order causing delays

Solution

1. Step 1: Understand streaming issues

   Streaming requires managing data flow to avoid overload, called backpressure handling.

2. Step 2: Identify cause of latency and loss

   If backpressure is not handled, data can pile up causing delays and loss.

3. Final Answer:

   Not handling backpressure in the streaming pipeline -> Option A

4. Quick Check:

   Streaming needs backpressure control [OK]

Hint: Streaming needs backpressure handling to avoid loss [OK]

Common Mistakes:

• Confusing batch with streaming
• Ignoring backpressure importance
• Assuming random access causes streaming issues

5. You design a video streaming service that must deliver smooth playback and allow users to jump to any timestamp instantly. Which storage access pattern combination is best?

hard

A. Sequential access for playback and batch access for buffering

B. Streaming access for playback and random access for seeking

C. Batch access for playback and sequential access for seeking

D. Random access for playback and streaming access for buffering

Solution

1. Step 1: Analyze playback needs

   Smooth playback requires continuous data flow, which is streaming access.

2. Step 2: Analyze seeking needs

   Jumping to any timestamp instantly requires random access to data at any position.

3. Step 3: Combine patterns for best design

   Use streaming for continuous playback and random access for quick seeking.

4. Final Answer:

   Streaming access for playback and random access for seeking -> Option B

5. Quick Check:

   Playback = streaming, seeking = random [OK]

Hint: Streaming for play, random for jump [OK]

Common Mistakes:

• Using sequential for seeking which is slow
• Confusing batch with streaming for playback
• Ignoring random access need for seeking