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Managed Disks vs Virtual Machine Disk Space

    Question

  • I am looking at a VM right now that is the L16 with 2.8 TB of disk space.  I have a database that I am considering moving to the cloud that is 1.4 TB.  I am looking at the L16 because it is one of the few Virtual Machines with storage space over 1.4 TBs.

    But there is also an option to select "Managed Disks"  Which seems like it can give a disk up to 1 TB.  I could probably use a few of those to fill my storage needs.

    But I am confused.  The pricing for a "Managed Disk" is much cheaper than the pricing difference between two Virtual Machines with higher and lower disk size.

    So I am wondering if "Managed Disks" are really something else and not a real storage option.

    Can anyone tell me if the managed disks are actual storage space that I could put a SQL Server database file on?


    • Edited by Vaccanoll Tuesday, April 4, 2017 8:09 PM
    Tuesday, April 4, 2017 8:08 PM

Answers

  • There are different types of storage you can use with VM's, for different purposes.

    The 2.8TB of space advertised on the L16 is local storage, this is the D drive on the VM and is storage passed directly from the host into the VM, because of this this storage is temporary, if you turn off your VM and turn it back on, this storage may be wiped. Because of this it's not really suitable for SQL usage. The L series are designed for things like Mongo DB which can use the large amounts of temporary space.

    For persistent storage you are going to want to attach data disks to your VM. This has two configurations the older storage account based disks, where you create a storage account and store VHD's in it, and then Managed disks, which are still VHD's, but you don't have to deal with the underlying storage etc, it's much simpler and I would recommend you use them. Disks have a maximum size of 1TB, but VM's can have multiple disks attached (how many depends on the size of teh VM), so if you need larger disks space you attache multiple disks adn join them together using something like storage spaces in Windows.

    Finally, when you choose the storage for your disks, there are also two storage types, standard and premium. Premium storage is much faster than standard, it's also recommended to use that for production work loads. I would suspect your SQL use is going to need premium storage.

    I hope that all makes sense, there's a lot of concepts. Let me know if you want me to go over anything in more detail.


    Sam Cogan Microsoft Azure MVP
    Blog | Twitter


    • Edited by SamCoganMVP Tuesday, April 4, 2017 8:57 PM
    • Marked as answer by Vaccanoll Tuesday, April 4, 2017 9:11 PM
    Tuesday, April 4, 2017 8:56 PM

All replies

  • There are different types of storage you can use with VM's, for different purposes.

    The 2.8TB of space advertised on the L16 is local storage, this is the D drive on the VM and is storage passed directly from the host into the VM, because of this this storage is temporary, if you turn off your VM and turn it back on, this storage may be wiped. Because of this it's not really suitable for SQL usage. The L series are designed for things like Mongo DB which can use the large amounts of temporary space.

    For persistent storage you are going to want to attach data disks to your VM. This has two configurations the older storage account based disks, where you create a storage account and store VHD's in it, and then Managed disks, which are still VHD's, but you don't have to deal with the underlying storage etc, it's much simpler and I would recommend you use them. Disks have a maximum size of 1TB, but VM's can have multiple disks attached (how many depends on the size of teh VM), so if you need larger disks space you attache multiple disks adn join them together using something like storage spaces in Windows.

    Finally, when you choose the storage for your disks, there are also two storage types, standard and premium. Premium storage is much faster than standard, it's also recommended to use that for production work loads. I would suspect your SQL use is going to need premium storage.

    I hope that all makes sense, there's a lot of concepts. Let me know if you want me to go over anything in more detail.


    Sam Cogan Microsoft Azure MVP
    Blog | Twitter


    • Edited by SamCoganMVP Tuesday, April 4, 2017 8:57 PM
    • Marked as answer by Vaccanoll Tuesday, April 4, 2017 9:11 PM
    Tuesday, April 4, 2017 8:56 PM
  • That was a GREAT answer!  Thank you very much for clearing that up for me!

    You saved me from recommending the completely wrong setup for our databases.  

    • Edited by Vaccanoll Tuesday, April 4, 2017 9:12 PM
    Tuesday, April 4, 2017 9:11 PM
  • Hi Sam,

    If we use managed disks for storage spaces and use Azure Disk encryption.

    What is the preferred way to back up the VM with Disks. So that in case of Planned Failure we can recreated the VM's with the disks. Looks Azure site backup will not work with Azure Disk Encryption?.

    Is there any other method to back up the VM which has the ADE enabled.

    Appreciate your response.

    Thanks & Regards,

    Ram

    Thursday, April 6, 2017 3:41 PM
  • Unfortunately backing up managed disks using disk encryption, using Azure VM backup isn't supported at the moment, hopefully this will change soon. Given that, you've really only got two options:

    1. Use the Azure backup agent (also known as MARS agent) running  inside your VMs to back up the files in your VM's

    2. Look to see if there are any third party backup tools that can do VM level backup with encrypted manged disks. I suspect given that this is fairly new there will be limited choice.


    Sam Cogan Microsoft Azure MVP
    Blog | Twitter

    Wednesday, April 12, 2017 10:10 AM