Availability of data is one of the primary responsibilities of an enterprise class storage system, and a focal point for VMware’s efforts toward continual improvement. Therefore, with VMware vSAN™ 8 Update 1, we introduce the Enhanced data durability feature for planed maintenance when using RAID 5/6. In an vSAN Express Storage Architecture (ESA) cluster, when a host enters maintenance mode (EMM) using the “Ensure Accessibility” option, it will allow vSAN to write all incremental updates to another host in addition to the hosts holding the object data in a stripe with parity. This helps ensure the durability of the changed data if additional hosts participating in the storage of that object fail while the host in maintenance mode remains offline. Durability components also allow vSAN to merge the updated data more quickly into the stripe with parity, allowing clusters to regain the prescribed level of resilience more quickly during these maintenance activities.
This data durability enhancement significantly speeds up the time required to patch, or perform other maintenance on a vSAN cluster, especially at scale.
In vSAN 8 U1, durability components are introduced, and used under the following conditions:
•When a host holding an object has been placed into maintenance mode using the “Ensure Accessibility” EMM option.
•When the object is using RAID-5 or RAID-6 erasure coding
•When there is a sufficient fault domain to write the new or updated data to.
•For this release, durability components are not used in the following conditions:
•Unplanned failures of a host storage object data (e.g. host outage/offline)
•When an object is using RAID-1 mirroring
When there is insufficient fault domains to write the new or updated data to.