Linux VM on Hyper-V - Disk IO

Question

I have several Linux VMs running on:
WindowsEditionId : ServerDatacenter
WindowsProductName : Windows Server 2019 Datacenter
WindowsVersion : 1809
CsModel : ProLiant DL380p Gen8
CsNumberOfLogicalProcessors : 48
CsProcessors : {Intel(R) Xeon(R) CPU E5-2695 v2 @ 2.40GHz, Intel(R) Xeon(R) CPU E5-2695 v2 @
2.40GHz}
CsTotalPhysicalMemory : 360740823040
DeviceGuardAvailableSecurityProperties : {BaseVirtualizationSupport, DMAProtection}
RAID: HP P420i Controller

Running RAID 10

After a while, my Linux VMs run into an issue where they have several repeating instances of writing to the system journal. It seems like it is due to an IO issue.
Here are the VM disk settings:
Disk /dev/sda: 40 GiB, 42949672960 bytes, 83886080 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt

Are there any special settings I need to set on the hyperivsor or in the VM?

Answer 1

Hi,

Based on your screenshot, please first try to troubleshoot your issue with the guidance in the article below and as this article suggests, try to update your firmware of your SSD or your kernel:

https://askubuntu.com/questions/1173738/crash-systemd-journal-failed-to-write-entry-ignoring-read-only-file-system-on

Thanks for your support!

BR,
Joan

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Answer 2

Hi,

Thanks for posting on our forum!

Based on your descriptions, firstly, I suppose, the reason why repeating instances were wirtten to your system journal was because you ran RAID10 which would automatically backup your data into your mirrored disk (i.e. each instance will be duplicated when being stored). Here is an article which can help you better understand RAID10:

https://www.enterprisestorageforum.com/software/what-is-raid-10-how-raid-10-works/

(Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.)

In addition, after my research on Linux (don't know which version your Linux is), the IO setting is in default and if you do not have any other requirements for your IO setting, just let its default setting alone. Or, you can contact your Linux supporter for more details about your situation (should I increase IO if running RAID10?) But, also in my research, running RAID10 is recommended by Linux, so its default setting for IO should already take this situation into consideration.

Here is an article about default maximum IO size in Linux kernel:

https://longwhiteclouds.com/2016/03/06/default-io-size-change-in-linux-kernel/

(Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.)

Thanks for your support! If you have any new findings about this case, you are encouraged to share your ideas and findings here. Have a nice day! : )

BR,
Joan

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