Caching for disks is a critical aspect when planning and administering Azure for SAP workloads with regards to the AZ-120 examination. It delivers substantial benefits by offering high speed data access, redcution of latencies and optimizing overall system performance.
Disk Caching Concept
Disk caching is a powerful technology that utilizes high-speed volatile memory (RAM) to store frequently accessed data, minimizing I/O operations to the slower physical disk. Essentially, when a disk I/O operation is performed, the operating system checks if the data is present in the cache. If so, the request is served right from the cache instead of reaching out to the physical disk. If the data is not cached, it will retrieve from the disk, and this information is stored in cache for future use.
Disk caching offers performance benefits, especially for applications with read-intensive operations, such as SAP workloads in Azure. It can reduce disk latency and improve the speed of data retrieval, thereby enhancing the overall system response times.
Azure Managed Disk Caching
Azure Managed Disks offer three types of caching settings – None, Read Only, and Read Write.
- None: In this case, the guest OS’s read and write operations are directly executed on the storage.
- Read Only: This setting allows the read operations to be cached. Write operations are done directly to the storage disk.
- Read Write: Both read and write operations are cached.
The caching setting for Azure Managed Disks depends on the workload requirements. For example, SAP recommends the “None” disk caching for database files on Azure since SAP workloads are write-intensive.
Implementation of Disk Caching in Azure for SAP Workloads
Let’s look at how to implement disk caching with an Azure VM for SAP Workloads.
- You need to create an Azure VM. During setup, under the ‘Disks’ section, in ‘OS disk type,’ you can either choose SSD or HDD and specify your caching requirement: None, Read-only, or Read/write as per your requirement.
az vm create \
--resource-group myResourceGroup \
--name myVM \
--image UbuntuLTS \
--size Standard_D2s_v3 \
--os-disk-caching ReadWrite
- For existing disks, you can change caching settings by choosing the Disk in the Azure portal > Configuration > Host Caching, then select your preference: None, Read-only, or Read/write.
az disk update \
--name myDisk \
--resource-group myResourceGroup \
--caching ReadWrite
Remember, when designing and implementing disk caching for SAP workloads in Azure, always consider your workload characteristics, performance, and availability needs. Ensure regular monitoring and performance tuning based on your specific requirements.
A common example of disk caching in the context of Azure for SAP Workloads would be Azure NetApp Files where frequently accessed data will load quickly due to being held in the cache, while data that is less often accessed is kept in the slower NetApp storage layers.
Conclusion
Understanding the role of disk caching, how it affects the performance of SAP workloads, and how to implement it in Azure is important while preparing for the AZ-120 exam. With a well-designed disk caching strategy, you can optimize the system’s overall performance, minimizing response times and providing a better user experience in the Azure environment for SAP Workloads.
Practice Test
True or False: Caching can improve disk performance in Azure for SAP Workloads by temporarily storing the data that can be served high quickly.
- True
- False
Answer: True
Explanation: Caching improves the performance by reducing the data access time, which in turn improves the system performance.
True or False: Only reading from the disk can benefit from caching.
- True
- False
Answer: False
Explanation: Disk caching can improve performance for both read and write operations as data is temporarily stored in a cache before being written to the disk.
Which of these benefits can be achieved with Disk Caching?
- A) Reduced latency
- B) Increased throughput
- C) Improved I/O operations
- D) All of the above
Answer: D) All of the above
Explanation: Disk caching improves the response time by reducing the latency, increases the throughput by serving repeated requests quickly, and improves I/O operations by efficiently handling read and write requests.
True or False: Disk caching can always lead to improved system performance.
- True
- False
Answer: False
Explanation: Though disk caching generally does improve system performance, in cases where the cache is misconfigured or the cache size is too small to be effective, it may not result in performance improvement.
In Azure, Shared Disk, Premium SSD, Standard SSD, and Standard HDD all support disk caching
- A) True
- B) False
Answer: A) True
Explanation: Azure provides various disk types that support disk caching, including Shared Disk, Premium SSD, Standard SSD, and Standard HDD.
Disk caching is not advisable in which of the following scenarios?
- A) When the same data is accessed multiple times
- B) When data is rarely reaccessed
- C) When latency needs to be minimized
- D) When throughput needs to be increased
Answer: B) When data is rarely reaccessed
Explanation: Disk Caching is less beneficial when data is rarely reaccessed, as it leverages frequently accessed data to boost performance.
What kind of disk caching improves read operations in Azure?
- A) Read-only caching
- B) Write-only caching
- C) Read-write caching
- D) None of the above
Answer: A) Read-only caching
Explanation: Read-only caching improves the performance of read operations by storing frequently accessed data in cache memory.
What kind of disk caching improves write operations in Azure?
- A) Read-only caching
- B) Write-only caching
- C) Read-write caching
- D) None of the above
Answer: C) Read-write caching
Explanation: Read-write caching improves the performance of both read and write operations by storing data in cache before it is written to disk.
Disk caching can be used as a primary method of data persistence.
- A) True
- B) False
Answer: B) False
Explanation: Disk caching is not a primary method of data persistence, but rather a way to enhance performance by reducing the data access time to frequently accessed data.
True or False: Caching policy cannot be set at the disk level in Azure.
- True
- False
Answer: False
Explanation: In Azure, you are allowed to change the caching policy at the disk level.
Using caching in Azure for SAP workloads can help in reducing costs associated with read and write operations.
- A) True
- B) False
Answer: A) True
Explanation: Caching can help reduce the costs associated with read and write operations by lowering the number of transactions made on the main disk.
Which Azure feature allows you to set caching policy at the disk level?
- A) Azure Disk Encryption
- B) Azure Backup
- C) Azure Blob Storage
- D) Azure Managed Disks
Answer: D) Azure Managed Disks
Explanation: Azure Managed Disks allow you to set the caching policy at the disk level.
In Azure, what is the maximum size of a single cache that can be created for disks?
- A) 256 GB
- B) 512 GB
- C) 768 GB
- D) 1 TB
Answer: B) 512 GB
Explanation: In Azure, a single cache can be created up to a size of 512 GB for disks.
True or False: Disk caching can be configured for Azure Blob Storage.
- True
- False
Answer: False
Explanation: Disk caching does not apply to Azure Blob Storage, as it is a separate service that doesn’t use disks in the same way virtual machines do.
Caching cannot be used with which type of Azure Disks?
- A) Premium SSD
- B) Standard SSD
- C) Standard HDD
- D) The above disks all support caching
Answer: D) The above disks all support caching
Explanation: Azure supports disk caching for all types of disks including Premium SSD, Standard SSD, and Standard HDD.
Interview Questions
What is caching in the context of disk storage?
Caching in the context of disk storage is a technology that enables the storage of frequently accessed data in high-speed media for efficient retrieval. It supports faster data access by keeping often-used data in a place where it can be accessed more quickly.
What is the primary purpose of implementing caching for disks in Azure?
The primary purpose is to improve the performance of Azure applications by reducing the time it takes to read from or write to disk storage. It also decreases latency.
Which Azure storage redundancy option should be used for SAP HANA workloads?
According to Microsoft's documentation, for SAP HANA workloads, it is recommended to use zone-redundant storage (ZRS).
What are the different types of caching available in Azure disk storage?
Azure Disk Storage offers three types of caching: Read-Only, Read-Write, and None.
How does read-only caching in Azure Disk Storage function?
In Read-Only caching, data is cached when read but writes are written directly to the disk. This reduces the load on the storage account and improves read performance.
What is the benefit of using read-write caching in Azure Disk Storage?
Read-Write caching improves both read and write operations by caching read data and buffering write data. This is highly beneficial for workloads with random writes.
In what scenario would it be beneficial to select ‘None’ for caching in Azure Disk Storage?
Selecting ‘None’ would be beneficial when a workload does not require a large amount of repetitive reads, such as a backup server, or when data integrity is paramount as it ensures data is written directly to the persistent disk before the write is acknowledged.
What is Azure Write Accelerator?
Azure Write Accelerator is a feature designed to improve the performance of large log write workloads, such as SAP HANA. It does this by allowing applications to commit writes to disk more quickly.
What factors should be considered when designing and implementing caching for disks in Azure with SAP workloads?
When designing and implementing caching for Azure with SAP workloads, you should consider the specific demands and performance goals of your SAP applications, the cache type that best suits your workload (read, write, or none), and the capacity of the Azure disk storage.
How can you enable Azure Write Accelerator for a disk?
Azure Write Accelerator can be enabled for a disk via the Azure portal, Azure CLI, Azure PowerShell or through an Azure Resource Manager template.
When would you use Azure’s Premium SSD storage for SAP workload?
Azure’s Premium SSD storage offers high-performance and low-latency disk support for Azure Virtual machines running IO-intensive workloads like SAP. They provide best-in-class IO latency and should be used when high throughput and low latency are required.
What Azure service would you use to deploy and manage disks used for SAP workloads in Azure?
Azure Disk Storage service would be used to deploy and manage disks used for SAP workloads in Azure. This service provides the option to choose between several disk storage types and offers different caching options to optimize performance.
What is Bursting in Azure Disk Storage and how can this be beneficial for SAP workloads?
Disk bursting in Azure Disk Storage enables your disk to burst its input/output operations per second (IOPS) and throughput (MB/s) for a short time daily, providing significant benefits for workloads that have bulk data transactions, such as SAP, by accommodating large amounts of intermittent traffic.
How do you enable or disable the caching type for an Azure disk?
The caching type for an Azure disk can be enabled or disabled via the Azure portal, Azure CLI, or Azure PowerShell. The cache setting is a property of the virtual machine’s disk attachment and not the disk itself.
Can caching be changed for an Azure Managed Disk that is attached to a running VM?
To change the caching setting of an Azure Managed Disk that's attached to a running VM, you need to first stop (deallocate) the VM. After changing the caching setting, the VM can then be started again.
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