PowerHA and LVLT4i.

We have had a number of conversations about LVLT4i and what it offers to the Managed Service Provider(MSP). As part of those discussions the IBM solution PowerHA often comes up as it also uses iASP technology but that is really where the similarity ends.

PowerHA uses the iASP to isolate the objects that are to be replicated to another system/storage device and it has an exact copy of the iASP from the source on the target. Changes are captured at the hardware level and are sent to the remote system as they occur.

LVLT4i only replicates objects to a remote iASP, it uses either Audit journal triggers or the Remote Journal technology to capture and send the data. The source object resides in *SYSBAS and the target object in an iASP, it is used primarily to allow multiple copies of the same library/object combination to be stored on a single system. The remote iASP is always available to the user.

iASP is not widely implemented at customer sites, this is in part due to the lack of support for iASP’s built into many of the applications that run on the IBM i today (many of the applications were built before iASP technology was available). For a customer to migrate an application to allow iASP use there are a number of constraints which have to be considered plus each users environment has to be adjusted to allow the iASP content to be used (SETASPGRP etc). This has further limited the use of iASP as many do not feel the benefits of moving to the iASP model out-weight the cost of migration. Another issue is you are now adding an additional storage management requirement, the iASP is disk based which will require protection to be added in some form. With LVLT4i you can leave your system unchanged, only the target system is going to need iASP setup and that will be in the hands of your Managed Service Provider. The decision about what to replicate is yours, with some professional help from a Managed Service Provider who knows your application it should be pretty bullet proof when it comes to recovery.

If you implement PowerHA you are probably going to need to set up an Admin Domain, this is where any *SYSBAS objects such as system values, profiles and configuration objects are managed. in LVLT4i we do not manage system values or configuration objects (configuration objects can be troublesome especially with TCP/IP) or system values. We have however just built in a new profile and password process to allow the security aspects of an application to be managed across systems in real time. Simple scripts can capture configuration and system value settings many of which are not important to your application so LVLT4i has you covered. If we find a need to build in system value or configuration management we will do so fairly rapidly.

PowerHA is priced by Core, so you license it for each Active Core on each system. Using CBU licensing, PowerHA can utilize lower active cores on the target and only activate them when the system is required. Unfortunately in a HA environment you are probably switching regularly so you will have the same number of active cores all the time. LVLT4i is priced by IBM tier regardless of the number of active cores. The target system license is included with the source system license regardless of the target system tier so a Manage Service Provider who has a P30 to support many P05 clients is not penalized.
PowerHA also comes in a few flavors which are decided on by the type of set up you require. Some of the functionality such as Asynchronous mirroring is only available in the Enterprise edition so if you need to ensure your application is not constrained by remote confirmation processing (waiting for the remote system to confirm it has the data) your are going to need the Enterprise edition which costs more per core. LVLT4i comes in one flavor and is based on a rental model, the transport of data over Synchronous/Asynchronous remote journals is available to all plus it supports any geographic model.

Because the iASP is always available the ability to backup at any time is possible with LVLT4i. With PowerHA you have to use a Flashcopy to make another disk based copy of the iASP which can then be used for the back up to tape etc. That requires a duplicate set of disks to match the iASP content. With LVLT4i you can use Save While Active or suspend the apply process for point in time saves, the remote journal will still be receiving your application updates which can be applied once the save has completed so data protection is not exposed.

RPO is an important number which is regularly banded around by the High Availability providers, PowerHA states it is 0 because everything is replicated at the hardware level. We believe LVLT4i is pretty close to the same but there are a couple of things to consider.

First of all, RPO of 0 will require synchronous delivery of changes, if you use an Asynchronous delivery method queued changes will affect that for either solution. LVLT4i uses Remote journalling for data changes, so if you use Synchronous mode I feel the two are similar in effect.

Because we use a different process for object changes, any object updates are going to be dependent on the level of change activity being processed by the object replication processes. The amount of data being replicated is also a factor as a single stream of object changes is used to transfer the updates. We have done a lot of work on minimizing the data which has be be sent over the wire such as using commands instead of save restore, pipe-lining changes so multiple updates to an object are optimized into a single action and compression within the save process. This has greatly reduced the activity and therefore bandwidth requirements.

PowerHA is probably better at object replication because of the technology IBM can access, plus it is going to be carried out in line with the data changes. The same constraints about using synchronous mode affect the object replication process so bandwidth is going to be a major factor in the speed of replication etc. Having said that, most of the smaller clients we have implemented any kind of availability for (HA4i/DR4i) do not see significant object activity and little to no backlogs in the object replication process.

The next recovery figure RTO talks about how long it will take from making the decision to switch, to actually switching. My initial findings about iASP tended to show a fairly long role-swap time because you had to vary off the iASP and then on again to make it available. We have never purchased PowerHA so our tests are based around how long it took to vary off and then on again a single iASP on our P05 system (approximately 20 minutes). I would suspect the newer and faster systems have reduced the time it takes but it is still a fairly long time. LVLT4i is not a contender in this role because we expect the role-swap times to be pretty extended (4 – 12 hours) even if you do a lot of automation and preparation.

One of the issues which affect all High Availability Solutions is the management of batch, if you have a batch process running at the time of failure it could affect the integrity of the application data on the target system. LVLT4i and PowerHA both have this limitation as the capture of job queue content is not possible even in an iASP, but we have a solution which when integrated with LVLT4i will allow you to reload job queues and identify orphaned data which has been applied by a batch process. Our JQG4i product captures all activity for specific job queues and will track each job from load to completion. This will allow you to recover the entire application environment to a known start point and thereby ensure your data integrity is maintained. Just being able to automatically reload jobs that did not run before the system failure is a big advantage that many current users benefit from.

There are plenty of options out there to choose from but each has its own strengths and weaknesses. LVLT4i uses the same replication technology as out HA4i and DR4i products with enhancements to allow the use of iASP as the target disk. It is not designed to meet the same RTO expectations as PowerHA even though both make effective use of iASP technology. However, PowerHA is not necessarily the best option for everyone because it does have a number of dependencies that make it more difficult/costly to implement than a logical replication solution, you have to weigh up the pros and cons of each technology and make a decision about what is important.

If you are interested in knowing more or would like to see a demo of the LVLT4i product please let us know and we will be happy to schedule.

Chris…