SEsparse Snapshot Data Inconsistencies

SEsparse snapshot data inconsistencies have been reported with databases. This is one of last week’s more interesting knowledge base articles. This is not something to take lightly. The knowledge base article is titled ‘Virtual Machines running on an SEsparse snapshot may report guest data inconsistencies (59216)’ . The good news is that it has been resolved and there is also a workaround. Please click on the link to see the entire kb article that includes the workaround.

Symptoms

  • Applications such as databases may report block-level data inconsistency.
  • Guest operating systems may report file system metadata inconsistencies
  • The VM fails to boot when it is running from an SEsparse snapshot.

SEsparse is a snapshot format introduced in vSphere 5.5 for large disks, and is the preferred format for all snapshots in vSphere 6.5 and above with VMFS-6.

Cause

VMware has identified an issue in SEsparse VM snapshots that can cause data inconsistencies.

This issue occurs when a VM is running on an SEsparse snapshot and experiences a burst of non-contiguous write IO in a very short period of time.

Impact / Risks

Impacted Configurations:

  • VMFS-5 or NFS Datastores: VMs with virtual disks >2TB and snapshots. On VMFS-5 and NFS, the SEsparse format is used for virtual disks that are 2 TB or larger
  • VMFS-6 Datastores: VMs with snapshots. SEsparse is the default format for all snapshots on VMFS-6 datastores.

Impacted vSphere releases:

  • vSphere 6.5 and above with VMFS-6 and any VM with snapshots.
  • vSphere 5.5 and above when VMs with virtual disks >2TB have snapshots.

Note: VMFS-5 or NFS datastores only use SEsparse with snapshots when virtual disks exceed 2 TB in size or SEsparse is explicitly configured.

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Resolution

The issue is resolved the following releases:

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