Comparison of PowerHA data resiliency technologies
Data resiliency allows data to remain available to
applications and users even though the system that originally hosted the data fails. Choosing the
correct set of data resiliency technologies in the context of your overall business continuity
strategy can be complex and difficult. It's important to understand the different data resilience
solutions that can be used to enhance availability in multiple system environments. You can either
choose a single solution or use a combination of these technologies to meet your needs. The
following topics compare and contrast the different data resiliency technologies within the PowerHA® product.
- Logical replication
Logical replication makes and keeps the objects on your production and backup systems identical. For journaled objects, the transactional operations on the source are duplicated on the target by applying journal changes. For non-journaled data, the changed data is saved and then written on the target. These apply processes on the target are provided by the logical replication. - Switched disk
Switched disk allow data that is stored in the independent disk pool to be switched between systems provides a level of data resiliency. - Switched logical unit
Switched logical units(LUNs) allows data that is stored in the independent disk pool from logical units that are created in an IBM DS8000®, SAN Volume Controller, or Storwize® to be switched between systems providing high availability. Switchable LUNs are a set of disk units in an independent disk pool that is controlled by a device cluster resource group and can be switched between nodes within a cluster. When switched LUNs are combined with IBM i clusters technology, you can create a simple and cost effective high availability solution for planned and some unplanned outages. - Geographic mirroring
Geographic mirroring is a function of the IBM i operating system. All the data that is placed in the production copy of the IASP is mirrored to a second IASP on a second, perhaps remote system. The replication is done within the operating system, so this solution can be used with any type of storage. There is both a synchronous and asynchronous version of geographic mirroring. Synchronous geographic mirroring guarantees that the two copies of the data are identical, but has a distance limitation, since the IO transaction will not complete on the source system until the IO has also reached the target system. Asynchronous geographic mirroring has no distance limitation, but if the source side fails unexpectedly, there may be a few seconds of data loss. - Metro Mirror
Metro mirroring is a function of the IBM System Storage® Server. The data that is stored in IASPs is on disk units that are in the System Storage Server. This solution involves replication at the hardware level to a second storage server that uses IBM System Storage Copy Services. Each storage server is attached to a different IBM i. An IASP is the basic unit of storage for the System Storage Peer-to-Peer Remote Copy (PPRC) function. PPRC provides replication of the IASP to another System Storage Server. IBM i provides a set of functions to combine the PPRC, IASPs, and IBM i cluster resource services for coordinated switchover and failover processing through a device cluster resource group (CRG). You can combine this solution with other System Storage based copy services functions, including switchable LUNs and FlashCopy® for save window reduction. - Global Mirror
Global Mirror uses the same base technology as Metro Mirror except the transmission of data is done in an asynchronous manner. Global Mirror on the DS8000 and with SAN Volume Controller and Storwize system change volumes requires a third set of disks to maintain data consistency. - DS8000 Full System HyperSwap
Full System HyperSwap® is a full system solution that allows for logical units that are mirrored between two IBM System Storage DS8000 units. The IBM i may switch the access from the primary DS8000 to the secondary DS8000 with minimal outage during this time, providing a minimal impact high availability solution. - DS8000 HyperSwap with independent auxiliary storage pools (IASPs)
PowerHA Enterprise Edition supports DS8000 HyperSwap at an IASP level. HyperSwap functions independently for SYSBAS and IASPs. HyperSwap relationships can be configured for SYSBAS logical units only, IASP logical units only, or both. - FlashCopy
FlashCopy is a function of the IBM System Storage server. FlashCopy provides a fast point in time copy of the data, which can be brought online on a separate partition or system. This copy can be used for offline backups or for populating data to a development or test system. FlashCopy can be used with any of the other data resiliency technologies included in PowerHA, or can be used separately.
Related concepts: