Resolving Incorrect Rotational Flag for Azure SSD in Ceph OSD Configuration

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Why do I encounter an Incorrect Rotational Flag for Azure SSD in Ceph OSD?

Issue Description

An Azure known issue incorrectly shows the rotational flag enabled for the Azure SSD disk. As a result, the Azure disk is not marked as SSD, and the following error occurs when trying to configure the Objectstore disk:

[ERROR][2022-08-18T05:26:35+0000]: Rotational device: '/dev/sdf' is not recommended for ceph OSD

Root Cause

Azure SSD disks are sometimes incorrectly labelled as rotational. This prevents Ceph from recognizing them as SSDs, impacting performance and functionality. Additionally, if an incorrect device is marked (e.g., sdf instead of sdd), the issue may persist despite configuration changes.

Resolution

To fix this issue and mark the Azure SSD disk as non-rotational, follow these steps:

  1. Run the Following Commands to Update the Rotational Flag
echo "0" > "/sys/block/{raw_device_name}/queue/rotational"

echo "KERNEL=="${raw_device_name}", ATTR{queue/rotational}="0"" >> "/etc/udev/rules.d/99-ceph-raw-osd-mark-ssd.rules"


udevadm control --reload


udevadm trigger

Example: 

echo "0" > "/sys/block/sdf/queue/rotational"

echo "KERNEL=="sdf", ATTR{queue/rotational}="0"" >> "/etc/udev/rules.d/99-ceph-raw-osd-mark-ssd.rules"


udevadm control --reload


udevadm trigger

  1. Verify the Disk Mapping

Run the following commands to check which devices are mapped:

ls -l /dev/uipath/ceph/

lsblk -o NAME,KNAME,TYPE,MOUNTPOINT,LABEL

Now, for example, If /dev/uipath/ceph/sdf is incorrectly pointing to sdf instead of sdd(assuming sdd was rotational flag enabled for the Azure SSD disk and accidentally, sdf was marked which causes issues during installation/prereq check), continue to the next step.

  1. Correct the Symlink If Necessary

If the output confirms an incorrect symlink, remove and recreate it:

rm -f /dev/uipath/ceph/sdf

ln -s /dev/sdd /dev/UiPath/ceph/sdd

Verify the changes:

ls -l /dev/uipath/ceph/

  1. Reload Udev Rules and Apply Changes

Since the file /etc/udev/rules.d/99-ceph-raw-osd-mark-ssd.rules was updated, reload and apply udev rules:

udevadm control --reload-rules

udevadm trigger

Confirm the changes:

cat /sys/block/sdf/queue/rotational

cat /sys/block/sdd/queue/rotational

Expected results:

  • sdf should show 1 (indicating an HDD)

  • sdd should show 0 (indicating an SSD)

If sdf still shows 0, reset it manually:

echo "1" > /sys/block/sdf/queue/rotational

  1. Reboot the System If Necessary

If changes do not reflect properly, reboot the machine:

sudo reboot

Following these steps will ensure that the correct disk is identified as an SSD and Ceph OSD can be configured without errors.