Blob storage (block, append, page) in Azure - Step-by-Step Execution

Process Flow - Blob storage (block, append, page)

Start: Choose Blob Type

↓

Append Blob Selected?

No→Page Blob Selected?

↓

Upload blocks

↓

Commit blocks

↓

Blob ready

↓

End

The flow starts by selecting the blob type. Depending on the type, data is uploaded differently: blocks for block blobs, appended for append blobs, and pages written for page blobs. Each ends with the blob ready for use.

Execution Sample

Azure

1. Select blob type: block
2. Upload block 1
3. Upload block 2
4. Commit blocks
5. Blob ready

This example shows uploading a block blob by uploading blocks and then committing them to finalize.

Process Table

Step	Action	Blob Type	Data State	Result
1	Select blob type	block	empty	Ready to upload blocks
2	Upload block 1	block	block 1 uploaded	Block stored temporarily
3	Upload block 2	block	block 1 and 2 uploaded	Blocks stored temporarily
4	Commit blocks	block	blocks committed	Blob finalized with blocks
5	Blob ready	block	committed blocks	Blob available for read/write
6	Select blob type	append	empty	Ready to append data
7	Append data chunk 1	append	chunk 1 appended	Data appended to blob
8	Append data chunk 2	append	chunks 1 and 2 appended	Data appended to blob
9	Blob ready	append	appended data	Blob available for append/read
10	Select blob type	page	empty	Ready to write pages
11	Write page 1	page	page 1 written	Page data updated
12	Write page 2	page	pages 1 and 2 written	Page data updated
13	Blob ready	page	written pages	Blob available for random read/write
14	Select blob type	invalid	empty	Error: Invalid blob type selected

💡 Execution stops after blob is ready or invalid blob type is selected.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
blob_type	none	block	block	block	block
data_state	empty	block 1 uploaded	block 1 and 2 uploaded	blocks committed	committed blocks
blob_status	not ready	not ready	not ready	ready	ready

Key Moments - 3 Insights

Why do block blobs require committing blocks after uploading?

Because blocks are uploaded separately and only combined into a single blob after commit, as shown in steps 2-4 in the execution_table.

Can you append data to a block blob directly?

No, appending data is only supported by append blobs. Block blobs require uploading blocks and committing them, as seen in the execution_table steps for append vs block blobs.

Why must page blobs write data in pages?

Page blobs store data in fixed-size pages allowing random read/write access, so data must be written in page-sized chunks, as shown in steps 11-12.

Visual Quiz - 3 Questions

Look at the execution_table, what is the data_state after step 3?

A block 1 uploaded

B block 1 and 2 uploaded

C blocks committed

D empty

💡 Hint

Check the 'data_state' column for step 3 in the execution_table.

At which step does the blob become ready for append blob type?

A Step 9

B Step 7

C Step 8

D Step 6

💡 Hint

Look for 'Blob ready' with blob type 'append' in the execution_table.

If you select an invalid blob type, what happens according to the execution_table?

A Blob is ready immediately

B Data is uploaded anyway

C Error: Invalid blob type selected

D Blocks are committed automatically

💡 Hint

Check the last row of the execution_table for invalid blob type behavior.

Concept Snapshot

Blob storage types:
- Block blobs: upload blocks, then commit to finalize.
- Append blobs: append data chunks sequentially.
- Page blobs: write fixed-size pages for random access.
Choose type first, then upload data accordingly.
Each type suits different storage needs.

Full Transcript

Blob storage in Azure has three types: block, append, and page blobs. The process starts by selecting the blob type. For block blobs, you upload data in blocks and then commit these blocks to finalize the blob. Append blobs allow you to add data chunks sequentially without committing. Page blobs store data in fixed-size pages, enabling random read and write access. If an invalid blob type is selected, an error occurs and the process stops. This flow ensures data is stored efficiently based on the blob type chosen.

Practice

1. Which type of Azure Blob storage is best suited for storing large files that are uploaded in blocks and can be updated by replacing blocks?

easy

A. Append blob

B. Page blob

C. Block blob

D. File blob

Solution

1. Step 1: Understand block blob usage

   Block blobs are designed to store large files uploaded in blocks and allow updating by replacing blocks.

2. Step 2: Compare with other blob types

   Append blobs are for append-only operations, and page blobs are optimized for random read/write operations, not block uploads.

3. Final Answer:

   Block blob -> Option C

4. Quick Check:

   Block blob = large files in blocks [OK]

Hint: Block blobs store large files in blocks, perfect for uploads [OK]

Common Mistakes:

• Confusing append blob with block blob
• Thinking page blob is for block uploads
• Selecting non-existent blob types

2. Which of the following is the correct way to create an append blob using Azure CLI?

easy

A. az storage blob create --container-name mycontainer --name myappendblob --type AppendBlob

B. az storage blob create --container-name mycontainer --name myappendblob --type BlockBlob

C. az storage blob create --container-name mycontainer --name myappendblob --type PageBlob

D. az storage blob create --container-name mycontainer --name myappendblob --type FileBlob

Solution

1. Step 1: Identify correct blob type syntax

   The Azure CLI uses --type AppendBlob to create an append blob.

2. Step 2: Verify other options

   BlockBlob and PageBlob are valid types but not for append blobs; FileBlob is invalid.

3. Final Answer:

   az storage blob create --container-name mycontainer --name myappendblob --type AppendBlob -> Option A

4. Quick Check:

   Append blob creation uses --type AppendBlob [OK]

Hint: Use --type AppendBlob to create append blobs in Azure CLI [OK]

Common Mistakes:

• Using BlockBlob type for append blobs
• Using PageBlob type for append blobs
• Using invalid blob type names

3. Consider this code snippet using Azure SDK to upload data to a blob:

blob_client = container_client.get_blob_client('myblob')
blob_client.upload_blob(data, blob_type='PageBlob')

What will happen if the data size is not a multiple of 512 bytes?

medium

A. Upload will fail with an error about data size alignment

B. Upload will succeed with data padded to 512-byte boundaries

C. Upload will succeed but truncate extra bytes

D. Upload will convert data to block blob automatically

Solution

1. Step 1: Understand page blob requirements

   Page blobs require data size to be a multiple of 512 bytes for alignment.

2. Step 2: Analyze upload behavior

   If data size is not aligned, the upload will fail with an error about size alignment.

3. Final Answer:

   Upload will fail with an error about data size alignment -> Option A

4. Quick Check:

   Page blob data size must be multiple of 512 bytes [OK]

Hint: Page blobs need 512-byte aligned data size [OK]

Common Mistakes:

• Assuming automatic padding of data
• Thinking upload truncates data silently
• Believing blob type auto-conversion occurs

4. You have an append blob but your application tries to overwrite existing data instead of appending. What is the likely cause and fix?

medium

A. Using page blob API calls on append blob

B. Using append_block method instead of upload_blob

C. Creating the blob as a block blob instead of append blob

D. Using upload_blob with overwrite=True instead of append_block method

Solution

1. Step 1: Identify append blob usage

   Append blobs require using append_block to add data without overwriting.

2. Step 2: Analyze the overwrite behavior

   Using upload_blob with overwrite=True replaces existing data, not appends.

3. Final Answer:

   Using upload_blob with overwrite=True instead of append_block method -> Option D

4. Quick Check:

   Append blobs append with append_block, not upload_blob overwrite [OK]

Hint: Use append_block to add data, not upload_blob overwrite [OK]

Common Mistakes:

• Confusing append_block and upload_blob methods
• Creating wrong blob type
• Using page blob APIs on append blobs

5. You need to design a system that stores virtual machine disks requiring frequent random read/write operations with low latency. Which Azure blob type should you choose and why?

hard

A. Append blob, because it allows efficient appending of logs

B. Page blob, because it supports random read/write with 512-byte pages

C. Block blob, because it supports large file uploads in blocks

D. File blob, because it supports file system semantics

Solution

1. Step 1: Identify requirements for VM disks

   VM disks need frequent random read/write with low latency and page-level updates.

2. Step 2: Match blob type to requirements

   Page blobs support random read/write operations in 512-byte pages, ideal for VM disks.

3. Step 3: Exclude other blob types

   Block blobs are for large uploads, append blobs for append-only logs, and file blob is not a valid Azure blob type.

4. Final Answer:

   Page blob, because it supports random read/write with 512-byte pages -> Option B

5. Quick Check:

   VM disks use page blobs for random read/write [OK]

Hint: Page blobs support random read/write, perfect for VM disks [OK]

Common Mistakes:

• Choosing block blob for VM disks
• Confusing append blob with page blob
• Selecting non-existent file blob type