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Can someone tell me the main benefits and differences between Managed disks and Unmanaged disks, various pros and cons of the managed and unmanaged disk and how best can I use this?

AjayKumar
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deadtest
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4 Answers4

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I would like to highlight some of the benefits of using managed disks:

  1. Simple and scalable VM deployment: Managed Disks will allow you to create up to 10,000 VM disks in a subscription, which will enable you to create thousands of VMs in a single subscription.

  2. Better reliability for Availability Sets: Managed Disks provides better reliability for Availability Sets by ensuring that the disks of VMs in an Availability Set are sufficiently isolated from each other to avoid single points of failure.

  3. Highly durable and available.

  4. Granular access control: You can use Azure Role-Based Access Control (RBAC) to assign specific permissions for a managed disk to one or more users. Managed Disks exposes a variety of operations, including read, write (create/update), delete, and retrieving a shared access signature (SAS) URI for the disk.

  5. Azure Backup service support: Use Azure Backup service with Managed Disks to create a backup job with time-based backups, easy VM restoration and backup retention policies.

  6. Are unmanaged disks still supported: Yes. Both support unmanaged and managed disks. We recommend that you use managed disks for new workloads and migrate your current workloads to managed disks.

Refer Azure Managed Disks Overview for more details.

Guido
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AjayKumar
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    But isn't a managed disk a bit more expensive? Pricing is not mentioned. – JP Hellemons Feb 09 '18 at 08:14
  • The way I understand it, you are charged for the total capacity of a managed disk, not just the space consumed. It seems like you're paying a significant premium to avoid managing disks yourself; which is really not that difficult. – WillD Dec 17 '18 at 20:01
  • I see a slightly different trade-off-set: paged-blob unmanaged disks (UD) cost more than managed disks (MD) if all the MDs storage is used. And, since you can easily "expand" MDs or incrementally add new MDs (https://learn.microsoft.com/en-us/azure/virtual-machines/linux/expand-disks) then you can have the advantages of the MDs at approx. the same price and effort of a UD. Also, AzureFileStorage (AFS) is convenient but is priced at Std. SDD prices. So if you can live with HDD, then MD-HDD is about half the AFS price. – GGleGrand Dec 29 '18 at 20:15
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    Managed disks are really slow; you have the perf you pay for which is poor for more money; If you are using SQL Server or any other db on a vm do not use managed disks, add the disks yourself and then 'stripe' them using "Windows Storage Spaces" to multiply your IOPS for less cost and way more perf. – Dan Oct 18 '19 at 08:43
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    @Dan what evidence is your comment based on? If you choose the same disk configuration, why would it have worse perf? – Prashanth Subramanian Apr 30 '20 at 08:56
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Essentially, Managed Disks are easier to use because they don't require you to create a storage account. I think Azure still creates one, but this detail is hidden from you.

The benefit of not having to manage a storage account is that storage accounts have limits, like max IOPS, so that if you place too many disks in a storage account, it is possible that you will reach the IOPS limit. Azure takes care of this for you.

If you have VMs in an Availability Set, Azure will make sure that disks are on different "stamps" ensuring that disks are spread out so that you don't have a single point of failure for the disks.

As for a Con, I've encountered two (but there are probably more):

  1. When taking snapshots they are Full Snapshots, not incremental, so this adds to storage cost.

  2. If you are setting up a Disaster Recovery between two Azure regions, using Recovery Services, managed disks are not yet supported.

    • Managed disk for Azure site recovery is now supported
Priyanka Rudramaina
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Andy T
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  • *so that if you place too many disks in a storage account, it is possible that you will reach the IOPS limit* Thanks for this, but could you expand on that? I am assuming that disks which are not actually being used by any VMs and are just left over in the storage account will not affect the IOPS limit.. is that correct? – Paolo Oct 10 '19 at 08:16
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Managed and unmanaged drives in Azure are different concept.

Unmanaged approach treat the drive as a service provided under storage account, you can use this "service" connecting it to your VM but from management perspective is completelly different entity. Contrary to this approach managed drive is a HDD you connect to your VM, storage account behind it is managed by Azure, so you should get appropriate performance for your disk size. In fact because VMs have there own IOPS limits associatied with hardware profile size just resizing the disk will generally doesn't provide you better performance. Since managed drives are newer and more "sophisticated" service they are also more expensive.

If you are interested in this topic I did quite complete comparison based on options available over az command line options here. There is also nice practical differences summary here

Marcin Stolarek
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    When providing answers on StackOverflow, you don't want to link your entire answer out to outside sources, but instead provide the content in the answer and then link/cite the sources at the bottom of the answer. – Highway of Life Mar 09 '18 at 17:24
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    @HighwayofLife edited as you suggested. Thanks for poiting this out, I'm quite new to the community. – Marcin Stolarek Mar 19 '18 at 19:04
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Managed Disks:

The managed disk provides enhanced manageability and high availability which provides the following features.

Simple - Abstracts underlying storage account/blob associated with the VM disks from customers. Eliminates the need to manage storage accounts for IaaS VMs

Secure by default – Role based access control, storage encryption by default and encryption using own keys

Storage account limits do not apply – No throttling due to storage account IOPS limits

Big scale - 20,000 disks per region per subscription

Better Storage Resiliency - Prevents single points of failure due to storage Supports both Standard and Premium Storage disks

Unmanaged Disks:

Less availability: Unmanaged disks do not protect against single storage scale unit outage

Upgrading process is complex: If you want to upgrade from standard to premium on unmanaged disks, process is very complex.

Apart from this unplanned downtime, security is the downsides of the unmanaged disks. However, Cost differences between managed and unmanaged are based on your workload use case

Sajeetharan
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