Shulou(Shulou.com)06/02 Report--

[what is VSAN? ]

VSAN is a scalable distributed storage architecture based on vSphere kernel. VSAN builds the VSAN storage layer by installing flash memory and hard disk in the vSphere cluster host, which is controlled and managed by VSAN to form a unified shared storage layer for vSphere cluster.

Storage in the vSphere infrastructure is changing, and traditional LUN-based storage management mechanisms apply storage capacity to the data storage level. The underlying storage array does not understand virtualization or file systems. VMware's next generation policy-driven storage method is no longer based on traditional VMFS storage volumes, but on object storage system model, based on virtual data storage or distributed data storage.

[VSAN data storage analysis]

The VSAN data store is an object store that is presented to the vSphere host as a file system, and the object storage service mounts the volume from each host in the VSAN-enabled cluster. By presenting them as a single distributed shared data store visible on all nodes, VSAN simplifies storage configuration so that there is only one data store for virtual machines, which comes from the storage space on each vSphere host in the VSAN cluster.

Through disk group configuration, all virtual machine files are stored in a separate storage entity. This way of data storage is relatively safe, but when there is a flash disk or capacity disk failure, the data will be transferred to other nodes. During the transfer, other failures may also occur. North Asia data recovery engineers solved a VSAN storage crash. Failure in which the virtual machine is inaccessible.

[case Analysis of VSAN Storage crash]

The failure is a VSAN cluster composed of four dell servers, two disk groups on each server, one disk group is a SSD hard disk with 5 SAS hard drives, SSD does flash memory, SAS does capacity disk, and the capacity disk in a disk group on one node fails offline, and VSAN carries out data reconstruction and migration.

At this time, due to the power outage, the data migration was not completed. When the call came, the capacity disk in the other disk group was also offline by two failures, resulting in the failure of the entire data storage. The VSAN management console could be logged in, but all virtual machines could not be accessed.

[analysis of VSAN stored data recovery process]

First, make a read-only image of all the hard drives of the four nodes, including SSD flash drive and SAS capacity disk, and three offline hard disks due to failure. After the backup is completed, restore all the original disks to the server, and begin to analyze the underlying data storage structure to confirm the distribution information of the hard disk where the virtual machine resides.

Because the existing virtualization programs do not restore virtual machines according to the architecture of VSAN, engineers in North Asia are also doing corresponding program development to test the accuracy of data distribution information when analyzing the underlying data storage structure.

Analyze the two disk groups on each node separately, take a look at the corresponding relationship between the flash hard disk and the capacity disk in the disk group, each hard disk has a unique identification to correspond to each other, and interpret the hard disk ID information in the disk group according to the ID information of the hard disk.

1. Get the UUID of the disk and UUID of the disk group on each hard disk

2. Obtain the component information of the capacity disk according to the component information of the capacity disk in each disk group.

3. Extract the component bitmap according to the MAP position of the component recorded in the component information.

4. extract component data and cache data according to the bitmap of the component

5. Get the object and the order of the component according to the description information of the component, and merge the component into an object.

6. Extract data according to the object.

[analysis of recovery results of VSAN stored data]

The object can also be regarded as a volume, or it can be understood as a logical volume. Each VSAN object that exists on the data store is composed of multiple components, which are distributed in the disk groups configured on the cluster host. In the process of recovery, the information extraction of the components is a key step, because the components are an important part of each object, and the failure components are rarely damaged. The restored virtual machine can start normally, this fault resolution takes a long time to analyze the corresponding relationship between component bitmap and disk, but in the end, all the technical problems are solved, and the restored virtual machine starts normally, which satisfactorily solves the recovery of data loss caused by VSAN failure.

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