Windows Azure data disk mount point was changed after reboot

Question

_{Tuesday, October 18, 2016 4:36 PM}

Windows Azure VM has attached a temporary disk with mount point /dev/sdb1. And the attached data disk should have a mount point /dev/sdc1. It works perfectly when I first launch my VM.

However, I found that the mount point for temporary disk and attached data disk was swapped. /dev/sdb1 becomes the data disk and /dev/sdc1 becomes the temporary disk.

Why was that happened? Any idea on this? Thanks

All replies (1)

_{Tuesday, October 18, 2016 7:45 PM}

Hi Yee,

Thank you for posting here! We are happy to assist you.

It is very likely that the disk order changed in the Azure setup somehow.

To prevent such a situation, you could use the UUID or LABEL to mount your drives. To find the corresponding you can try blkid or ls -alh /dev/disk/by*

An entry in /etc/fstab would look like as follows.

UUID=c42c3d1d-1976-48c9-9a5b-45235f73edb3 /tempdata    ext4    defaults     0 1

LABEL=DATA                                /data        ext4    defaults     0 1

Please ensure that you adopt the mountpoints, LABEL and/or UUID contents and filesystem setting.

Understanding the temporary drive on Windows Azure Virtual Machines

By default, when creating a new VM, Azure will provide you an OS disk (/dev/sda) and a temporary disk (/dev/sdb), subsequently added disks will show as /dev/sdc, /dev/sdd and so on. Be aware that content on this disk may be lost in case of specific events like VM resizing or Azure Host OS failure. Even if content will survive VM reboots, should be considered a temporary storage. The size of temporary disk will vary depending on the VM size and SKU as listed at the link below. This disk is recommended to be used for the Linux swap file as you can read in the next point below.

Virtual Machine and Cloud Service Sizes for Azure

http://msdn.microsoft.com/en-us/library/azure/dn197896.aspx

Please write back if you have more questions.

Regards,
Sumanth BM