VMFS Recovery
Introduction
VMFS (Virtual Machine File System) recovery is a critical process aimed at restoring data stored within the VMFS file system, a specialized file system developed by VMware for use in ESX servers and vSphere virtualization environments. Designed primarily for the storage of virtual machine disk images, VMFS is optimized to manage a limited number of large files. This article delves into the intricacies of VMFS recovery, detailing the architecture, metadata, and recovery approaches.
VMFS Architecture
VMFS is designed to store disk images for ESX virtual machines, focusing on optimizing performance for a small number of large files. Disk space for a VMFS volume can be provided by a single disk or multiple disks, often organized as hardware RAID arrays. The VMFS driver consolidates these available disk space extents into a JBOD (Just a Bunch Of Disks) configuration, enhancing data management and retrieval.
VMFS Metadata
Metadata in VMFS is critical for file organization and retrieval. It is typically located at the beginning of the VMFS volume or, in the case of multiple extents, at the start of the first extent. VMFS metadata includes inodes, which store file information, directories, and repositories for small files.
To store disk images of virtual machines efficiently, VMFS employs 1 MB clusters, a cluster size larger than that used by most common file systems. As a result, without specific optimization, even small files occupy a minimum of 1 MB. However, with VMFS version 5 and beyond, files smaller than 1 KB are stored directly within their corresponding inodes, similar to how resident files are managed in the NTFS file system. For files larger than 1 KB, VMFS creates a single large file and divides it into 8 KB clusters, which are then utilized to store small files. These approaches effectively reduce disk space usage for small files. Notably, directories, regardless of their size, always occupy at least 1 MB of disk space.
It's important to mention that all VMFS metadata is typically contained within the first 3 to 5 GB of the VMFS volume. Consequently, a comprehensive VMFS structure recovery can be achieved by scanning only the initial 5 GB of the VMFS volume.
VMFS Recovery Approaches
VMFS recovery is a multifaceted process that aims to restore data from VMFS volumes, even in complex scenarios requiring preliminary RAID recovery. The VMFS recovery capability offered by Diskinternals VMFS Recovery© is instrumental in this regard, accommodating both straightforward and intricate recovery cases.
RAID Configuration Recovery: Since VMFS is often implemented on one or multiple hardware RAID configurations, the initial step in VMFS recovery is to recover the correct RAID storage configuration. This is achieved by detecting the configuration of one or more RAID arrays that compose a VMFS volume. The RAID recovery feature, known as RAID Wizard, is a step-by-step guide for this purpose.
VMFS File System Recovery: Once VMFS extents are correctly assembled, the process of VMFS file system recovery can commence on the reconstructed RAID disk volume. The reconstructed RAID disk, along with any automatically detected volumes it contains, is added to the disk list, marked in red to facilitate navigation.
Manual Assembly: In cases where the RAID volume is not detected automatically, manual assembly of the RAID volume from the physical volumes or disk images is possible. This is accomplished by running the RAID Wizard and specifying the necessary configuration for the RAID disk containing the VMFS volume.
Scanning for VMFS Volume: In situations where the VMFS volume is not initially detected, a scan can be initiated. VMFS Recovery is instructed to search for viable VMFS data on the disk, offering an inclusive approach to data retrieval.
In conclusion, VMFS recovery is a crucial process for the retrieval of data from VMFS volumes, whether the circumstances are straightforward or complex. Diskinternals VMFS Recovery© provides the necessary tools and guidance to ensure successful VMFS recovery, encompassing RAID configuration recovery, VMFS file system recovery, manual assembly, and comprehensive scanning approaches.