Product : DataCore, SSY [SDS]/10.0 PSP9, x86
Feature : Node Failure Protection, Reads/Writes, Data Availability
Content Owner:  Herman Rutten
2-way and 3-way Mirroring (RAID-1)
DataCore SANsymphony software primarily uses mirroring techniques (RAID-1) to protect data within the cluster. This effectively means the SANsymphony storage platform can withstand a failure of any two disks or any two nodes within the storage cluster. Inter-Node mirroring happens at the Virtual Disk level between pools.

The end-user is able to define which node is paired to which node for that particular Virtual Disk.

SANsymphony supports Dynamic Data Resilience. Data redundancy (none, 2-way or 3-way) can be added or removed on-the-fly at the vdisk level.

A 2-way mirror acts as active-active, where both copies are accessible to the host and written to. Updating of the mirror is synchronous and bi-directional.

A 3-way mirror acts as active-active-backup, where the active copies are accessible to the host and written to, and the backup copy is inaccessible to the host (paths not presented) and written to. Updating of the mirrors active copies is synchronous and bi-directional. Updating of the mirrors backup copy is synchronous and unidirectional (receive only).

In a 3-way mirror the backup copy should be independent of existing storage resources that are used for the active copies. Because of the synchronous updating all mirror copies should be equal in storage performance.

When in a 3-way mirror an active copy fails, the backup copy is promoted to active state. When the failed mirror copy is repaired, it automatically assumes a backup state. Roles can be changed manually on-the-fly by the end-user.