Resolving SCSI reservation conflicts

Products

VMware vSphere ESXi

Issue/Introduction

When experiencing any of the following symptoms on an ESXi host, SCSI reservation conflicts may be preventing access to storage devices:

Unable to access one or more datastores that were previously accessible
A host unexpectedly loses connection to a datastore
Unable to extend or increase the size of a datastore after it has been expanded at the storage level
Commands like vdf never complete or fail with timeout errors
Virtual machines on the affected datastores become inaccessible
RDM disks invisible in Windows VM
The following error appears when attempting to access a LUN:
Error messages in logs containing RESERVATION CONFLICT or Error status H:0x0 D:0x18 P:0x0

Failure reading partition table from device [naa.xxxxx]: I/O error

These issues can occur even when the LUN is properly zoned, presented, and configured.

Environment

vSphere ESXi 6.x
vSphere ESXi 7.x
vSphere ESXi 8.x
vSphere ESXi 9.x

Cause

SCSI reservation conflicts occur when one host in a cluster has placed a SCSI reservation on a LUN and has not released it. This can happen due to:

A SAN switch reboot during a reservation operation
Path failures during storage operations
Networking issues interrupting storage communications
Hardware failures
Duplicate HBA World Wide Names (WWNs) are assigned to multiple ESXi hosts. This leads to the same HBA WWN being incorrectly associated with various hosts within the backend storage's zoning configuration.

Resolution

1. To identify and resolve SCSI reservation conflicts, perform the following steps:

Run this command to confirm the ESXi host detects the LUN

esxcfg-scsidevs -c

- You should see output similar to:
  
  Device UID Device Type Console Device Size Plugin Display Name eui.################ Direct-Access /dev/sda 70007MB NMP Local FUJITSU Disk (eui.################) mpx.vmhba#:C#:T#:L# CD-ROM /dev/sr0 0MB NMP Local HL-DT-ST CD-ROM (mpx.vmhba#:C#:T#:L#) mpx.vmhba#:C#:T#:L# Direct-Access /dev/cciss/c0d0 34727MB NMP Local VMware Disk (mpx.vmhba#:C#:T#:L#)

If the LUN is not present, it is advisable to rescan the storage adapters.

2. To check for SCSI Reservation Conflict errors, examine the vmkernel log by running the following command:

cat /var/log/vmkernel.log | grep 'H:0x0 D:0x18 P:0x0'

Search for similar entries within the log:

scsi0 (0,0,52) : RESERVATION CONFLICT
NMP: nmp_ResetDeviceLogThrottling:3778: Error status H:0x0 D:0x18 P:0x0 Sense Data: 0x0 0x0 0x0 from dev "eui.############################"

The Device Status code 0x18 indicates a RESERVATION CONFLICT

3. To determine which host holds a reservation on the LUN, execute the following command on every host within the cluster:

esxcfg-info -s | grep -E 'Console Device|Is Reserved|Pending Reservations' | grep -B2 -E 'Pending Reservations.*[0-9]'

Look for output showing a non-zero "Pending Reservations" value:

|----Console Device....................../vmfs/devices/disks/eui.########################################
|----Is Pseudo...........................false
|----Is Reserved.........................true
|----Pending Reservations................ 1

The host showing "Pending Reservations" with a value greater than 0 is holding the lock.

4. Clear the reservation by performing a LUN reset on the affected device:

vmkfstools --lock lunreset /vmfs/devices/disks/eui.######################################################

5. Clear the reservation by performing a LUN reset on the affected device:

vmkfstools --lock lunreset /vmfs/devices/disks/eui.######################################################

Note: Replace the device path with the actual path to your device. For NAA IDs, use:

vmkfstools --lock lunreset /vmfs/devices/disks/naa.############################

7. Verify the lock was cleared by running the command again

esxcfg-info -s | grep -E 'Console Device|Is Reserved|Pending Reservations' | grep -B2 -E 'Pending Reservations.*[0-9]'

Ensure that "Pending Reservations" is now 0 and "Is Reserved" is false

|----Console Device....................../vmfs/devices/disks/eui.########################################
|----Is Pseudo...........................false
|----Is Reserved.........................false
|----Pending Reservations................ 0

8. Rescan storage on all hosts in the cluster

Verify datastore access is restored and operations like extending datastores can now be completed

If the datastore is unmounted, the backing LUN can be unpresented and represented to the hosts with a cluster rescan in between.

If the error persists after following these steps, contact Broadcom Support for further assistance.

Additional Information

In relation to step 3:

For an RDM LUN added as a disk to a VM cluster, we expect that on the active node, a SCSI reservation is held against the LUN as follows:
esxcfg-info -s | grep -E 'Console Device|Is Reserved|Pending Reservations' | grep -B2 -E 'Pending Reservations.*[0-9]'
...
|----Console Device....................../vmfs/devices/disks/eui.########################################
|----Is Pseudo...........................false
|----Is Reserved.........................true
|----Pending Reservations................ 0

On the hosts, on which passive VM nodes run, and on remaining hosts, we expect to see:
esxcfg-info -a | egrep "Is Reserved|Pending"
...
|----Console Device....................../vmfs/devices/disks/eui.########################################
|----Is Pseudo...........................false
|----Is Reserved.........................false
|----Pending Reservations................ 0
As such, for an RDM LUN, where there is a stale SCSI reservation (leading to SCSI reservation conflicts), if the host holding the reservation has not released it, we would expect to see the first pattern ("Is Reserved" = True).

Monitor reservation conflicts using ESXTOP.

Run esxtop
Press u to display the device list
Press f to add fields
Press H for Reserve State and press Enter
Look at RESV/s (Reservation / sec) and CONS/s (conflicts / sec)

Troubleshooting LUN connectivity issues on ESXi hosts

Performing a rescan of the storage on an ESXi host