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Understanding the VMkernel log message: FS3: Reached maximum number of holders (1015797)

Purpose

This article explains a limitation of VMFS Datastores with respect to sharing disks among multiple virtual machines.

Cause

This message indicates that the maximum number of eight (8) ESX/ESXi hosts are holding a lock on a given file on a VMFS 3 Datastore.

When non-exclusive locks are in use, multiple virtual machines can open and access a file's contents concurrently. This facilitates use cases such as:
  • Clustering virtual machines sharing read/write access the same virtual disk.
  • Linked clones of virtual machines sharing read-only access to the same parent virtual disk.
  • Virtual machines sharing read-only access to an ISO in a software or operating system repository.
A lock holder reference is maintained on the VMFS 3 Datastore file for each host running a virtual machine in the participating group. There are a maximum of eight lock holders possible for an VMFS 3 Datastore. This limits the virtual machines accessing a disk to a cluster of eight ESX/ESXi hosts, though the number of virtual machines running on those hosts, and accessing the same virtual disk, can exceed eight. This restriction applies to virtual disk (VMDK) files, ISO CD/DVD images, floppy images, or any other file.


Resolution

To work around this issue:

Note: With the introduction of a new locking mechanism in vSphere 5.1, the number of hosts that can share a read-only file on a VMFS volume has been increased to 32. For more information, see document VMFS File Locking and Its Impact in VMware® View™ 5.1

Additional Information

The first line of the logs under Symptoms indicates the desired lock type and the location of the file and heartbeat regions on disk. This information may be used to determine the file or the lock-holders. For additional information see Investigating virtual machine file locks on ESXi/ESX (10051)

This restriction is described in documentation for products which leverage shared disks on vSphere ESX/ESXi:
Note: In some cases the FS3: Reached maximum number of holders error can occur when ISOs are attached and connected to the CDROM drive in the virtual machine.

See Also

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