Microsoft Azure performs infrastructure maintenance for hosts on which Azure VM instances are running. For details, see Cloud platform maintenance (Cloud for Microsoft Azure) in the VSP One SDS Block and SDS Cloud System Administration.
This maintenance is performed at random by the infrastructure of Microsoft Azure. When the maintenance occurs, VSP One SDS Block automatically blocks the storage nodes of the affected VM instances.
After maintenance is completed, blockage of the storage nodes is automatically recovered. However, since redundancy is temporarily degraded, depending on the frequency of maintenance, the number of allowable storage node or drive failures may be exceeded, VSP One SDS Block may blocks the storage cluster as a result.
If the storage cluster is blocked, see the VSP One SDS Block and SDS Cloud Troubleshooting Reference for recovery procedures.
In addition, since it is unlikely that multiple VM instances in different Availability Zones will undergo maintenance simultaneously, the probability of the storage cluster blockage in Multi-AZ configuration is lower than the probability in Single-AZ configuration. In Single-AZ configuration, the probability of the storage cluster blockage with HPEC 4D+2P data protection is lower than the probability with MirroringDuplication data protection.
Therefore, the likelihood of storage cluster blockage is lowest for clusters with Multi-AZ configuration and MirroringDuplication data protection, followed by clusters with Single-AZ configuration and HPEC 4D+2P data protection, and highest for clusters with Single-AZ configuration and MirroringDuplication data protection.
For this reason, consider to use the storage cluster with Multi-AZ configuration and MirroringDuplication data protection.
Furthermore, when the number of storage nodes or drives is large, the probability of storage cluster blockage increases. Therefore, consider minimizing the number of storage nodes and drives as much as possible within the range that allows for sufficient performance, and instead use drives with larger capacities.