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VMware vSAN 6.2 handles erasure coding as a policy attribute that an administrator can apply to VM storage instances. An administrator can implement RAID 1, RAID 5 or RAID 6 as part of the policy.
For example, open the vSphere Web Client, select Policies and Profiles, and then click VM Storage Policies. Select the Create a new VM storage policy icon, and then select a vCenter Server. Enter a name and description for the new storage policy, and then click Next. This opens a new rule set dialog window. Select vSAN from the rules based on data services dropdown menu, and the administrator will then be able to configure all of the features that the vSAN data store allows. These features include the number of disk stripes per object, flash read cache preservation percentage, the number of failures to tolerate, the failure tolerance method, an IOPS limit for the object, the option to disable object checksum and force provisioning.
Although the dialog offers an array of possible settings, RAID protection involves only the number of failures to tolerate and the failure tolerance method entries.
To implement RAID 1, the administrator should set the failure tolerance method entry to RAID-1 (mirroring) – performance. Since RAID 1 mirroring demands fewer I/O operations to synchronize the duplicate -- mirrored -- disks, it usually offers better performance than RAID 5 or RAID 6. The administrator can set the number of failures to tolerate to one or even two, if RAID 1 is configured with two replicas rather than one.
Organizations that prefer to implement RAID 5 should set the failure tolerance method entry to RAID-5/6 (erasure coding) – capacity and set the number of failures to tolerate to one. To configure RAID 6, set the failure tolerance method to RAID-5/6 (erasure coding) – capacity, and set the number of failures to tolerate to two. Neither RAID 5 nor RAID 6 erasure coding supports a number of failures to tolerate value of three.
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