HOTSPOT
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You have an Azure subscription that contains a virtual machine named VM1.
To VM1, you plan to add a 1-TB data disk that meets the following requirements:
• Provides data resiliency in the event of a datacenter outage.
• Provides the lowest latency and the highest performance.
• Ensures that no data loss occurs if a host fails.
You need to recommend which type of storage and host caching to configure for the new data disk.
Answer: Storage type: Premium SDD that uses zone-redundant storage (ZRS) Host-caching: Read-only Rationale ZRS replicates to different locations Host caching: Write cache stores information in memory, no host, no memory, no data Redundancy options for Azure managed disks - Azure Virtual Machines | Microsoft Learn Enable and configure Azure VM disk cache with the Azure portal - Training | Microsoft Learn
For the cache question.. There is no guarantee to the data stored in Cache. Hence Read Only is advised. Only application that can bear minor data loss can go for Read/Write Cache. https://learn.microsoft.com/en-us/answers/questions/1350516/host-caching
I think it should be no cashing at all, from the same link you provided: Host caching is not a good choice for workloads that have the following characteristics: Write frequently to the disk. Cannot tolerate any data loss.
Host-caching: Read-only is correct. Writes are the only thing that's different with read/write caching. When writing with host caching is set to Read/write, the write only needs to be written to the host cache to be considered complete. The write is then lazily written to the disk when the cache is flushed periodically.Writes are the only thing that's different with read/write caching. When writing with host caching is set to Read/write, the write only needs to be written to the host cache to be considered complete. The write is then lazily written to the disk when the cache is flushed periodically.
Let's evaluate the requirements: 1. **Provides data resiliency in the event of a datacenter outage.** - Zone-redundant storage (ZRS) provides this capability by replicating data across multiple availability zones, ensuring that if one datacenter fails, the data is still available in other zones. 2. **Provides the lowest latency and the highest performance.** - Premium SSDs offer better performance and lower latency compared to Standard SSDs. 3. **Ensures that no data loss occurs if a host fails.** - Write caching can pose a risk of data loss in the event of a host failure. Thus, we need to be careful when enabling write caching. Given the options: Storage: - Premium SSD that uses zone-redundant storage (ZRS) is the right choice as it provides high performance and ensures data resiliency across datacenter outages. Host caching: To avoid data loss during a host failure, we should avoid using write caching. - Read-Only would be the appropriate choice to enhance performance without risking data loss due to host failure.
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PremiumSSD(ZRS)/Read-only
Premium SDD that uses zone-redundant storage (ZRS) Host-caching: none (no data loss) https://learn.microsoft.com/en-us/azure/architecture/example-scenario/identity/adds-extend-domain#vm-recommendations
"You can enable host caching when you create your virtual machine and attach disks. You can also turn on and off host caching on your disks on an existing VM. By default, cache-capable data disks will have read-only caching enabled. Cache-capable OS disks will have read/write caching enabled."
Here chatGPT's answer - To meet the given requirements of providing data resiliency, low latency, high performance, and ensuring no data loss in case of a host failure for the 1-TB data disk on VM1 in Azure, you should make the following recommendations: Storage type: 2. Premium SSD that uses zone-redundant storage (ZRS) Zone-redundant storage (ZRS) replicates your data across Availability Zones, which provides data resiliency in the event of a datacenter outage. Premium SSDs offer low latency and high performance compared to Standard SSDs. Host caching: 2. Read-only For this scenario, it's recommended to use Read-only host caching. Read-only caching can help improve read performance while ensuring data consistency and minimizing the risk of data loss. This aligns with the requirement to ensure that no data loss occurs if a host fails, as write caching (Read/Write) can have some risks associated with data integrity during host failures. Personally I think the both the answers are correct, and the reasoning is also accurate.
There is no details regarding type of workload will be placed on the data disk. This is a bad question. Let's go by the default. By default, cache-capable data disks will have read-only caching enabled. Cache-capable OS disks will have read/write caching enabled. https://learn.microsoft.com/en-us/azure/virtual-machines/disks-performance
Is Host-caching: None not perhaps the correct option? While Read-only caching reduces the risk, it doesn't entirely eliminate it because there's still potential for data loss in case of host failure before data is written to the disk. If data durability is a top priority and you want to minimize the risk of data loss in the event of host failure, is choosing the None caching option for the data disk not the safest choice?
Regarding the caching question: you can safely turn on read-only caching. Read-only caching will not lead to *more* data loss in the event of a host failure. Since we're going with ZRS, there is a redundant storage location we can read from. This combination ensures that no data loss occurs if *a* host fails.
- Premium SDD that uses zone-redundant storage (ZRS) Host-caching: Read-only
Here chatGPT's answer - To meet the given requirements of providing data resiliency, low latency, high performance, and ensuring no data loss in case of a host failure for the 1-TB data disk on VM1 in Azure, you should make the following recommendations: Storage type: 2. Premium SSD that uses zone-redundant storage (ZRS) Zone-redundant storage (ZRS) replicates your data across Availability Zones, which provides data resiliency in the event of a datacenter outage. Premium SSDs offer low latency and high performance compared to Standard SSDs. Host caching: 2. Read-only For this scenario, it's recommended to use Read-only host caching. Read-only caching can help improve read performance while ensuring data consistency and minimizing the risk of data loss. This aligns with the requirement to ensure that no data loss occurs if a host fails, as write caching (Read/Write) can have some risks associated with data integrity during host failures. Personally I think the both the answers are correct, and the reasoning is also accurate.