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Jerry Melnick

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Windows 2008: Blog Post

Q&A: Windows Server High Availability

How do you determine when to use an HA solution vs. a DR solution?

Thanks again to those who joined us for last week’s webinar, "Windows Server 2008 High Availability: Technology Comparison." The on-demand recording of last week's webinar is now available to watch at your convenience (here).

We had a lot of good questions from our attendees during the Q&A portion of the webinar, which are summarized below.

Q: How do you determine when to use an HA solution vs. a DR solution?
When it comes to availability vs. recovery, the most important question to ask is what are your recovery time objectives (RTO)? What is the amount of time your application can afford to be down? If the applications have strict requirements, then you want an availability solution. Disaster recovery is data replication often times with a failover capability, not availability. For critical applications, this may not be sufficient.

Q: If I have an HA solution in place, do I still need a solution for backup?
Availability and backup are two different things. That question comes up a lot, along with the need for disaster recovery. Backup will never likely go away completely. You still need to backup your data to ensure recovery in the future should that be necessary.

Q: Is everRun available for Linux applications?
Yes. We can provide basic failover capabilities for Linux applications today.

Q: How does everRun differ from replication solutions?
everRun 2G is used for availability, both locally and for short-distance geographic separation as well. We have a replication and recovery solution as well that can be used for disaster recovery for long distances. You should determine what your objectives are: do I have to keep my applications up and running or do I just need to recover it if something fails? What’s the recovery time objective for each application? It’s up to your individual applications and what level of protection you need for each. Often times availability is a priority as downtime is not desirable, with DR also a requirement on top of that to ensure recovery in the event of a major outage.

Q: Can everRun be used for planned downtime (i.e. to keep one host running for end-users while the application on the other host is being upgraded)?
Yes, everRun can be used to help facilitate certain system updates to reduce interruptions and mitigate risk.

Q: Can it work between two virtual machines and on x64 based systems?
Yes, we support XenServer and 64-bit hardware and Windows Server environments.

Q: What is the performance impact of using everRun 2G?
That’s variable depending on your application. It can be anywhere from 3-15%. We’ve done some performance testing specifically on XenApp and Exchange. You can download those white papers here:
Understanding and Characterizing Performance Implications for Running Exchange 2007 with everRun
XenApp 5.0 High Availability Performance

Q: Does Marathon offer backup solutions for everRun users?
We have methods to backup your systems and we’re working improving on our current offerings to make them quicker, easier and more granular.

Q: Can everRun work with dissimilar hardware? Can everRun work with more than two servers?
From a server standpoint, you just need similar processors; storage does not need to be similar. You can have SAN on one side and NAS on the other or any other combination. On the second question, yes, everRun will work with more than two servers. You can build a pool of servers and protect within that pool.

Q: Does everRun have backward compatibility with older OS?
Yes. It will work with Windows Server 2003, and also Windows Server 2008.

Q: What is the licensing model? Is it based on physical servers, CPUs, aggregate CPU count across servers, etc?

Licensing is per host, not per CPU or socket or processor. A pair of two hosts requires two licenses.

Q: Can everRun run on the Foundation Server Edition of Windows 2008?
It does not. everRun supports the full implementation of Windows Server 2008. everRun runs underneath Windows, it does not install into Windows.

Q: How does everRun handle data stored on NAS?
Storage is transparent to everRun. We look at storage as just a LUN.

Q: What is difference between everRun HA and everRun 2G in Windos Server 2003?
The differences are the ability to create multiple workloads. HA can protect one workload. everRun 2G can protect multiple workloads. There is also a new and improved graphical interface with better reporting and management capabilities.

Q: Does everRun work with XenServer 5.5?
Yes, everRun works with XenServer 5.5.

Q: Are there any changes in WS 2008 & WS 2008 R2 in the way that HA improves?
Yes. You can find an overview of those changes directly from David Hanna of Microsoft in our recent webinar and white paper “The Top 10 Reasons to Upgrade to Windows Server 2008.” You can also read the Q&A with Microsoft from that webinar here.

Q: Is everRun 2G available for Microsoft Hyper-v?
We will provide support for Hyper-v in a future release.

Q: With applications using various DNS names, how does this solution integrate with DNS changes? (failover to remote office for true DR-different IP/network)
everRun availability solutions pairs systems within the same subnet of vLAN, eliminating the need to make any DNS changes.

Q: Question is tied to what permissions are needed to do a recovery. For recovery in active Directory most items need to replicate around that there was a change and we do not want to hand out Admin control over the domain(separation of access)
everRun is designed to not require any changes to Active Directory during or after a failure or recovery.

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More Stories By Jerry Melnick

Jerry Melnick (jmelnick@us.sios.com) is responsible for defining corporate strategy and operations at SIOS Technology Corp. (www.us.sios.com), maker of SIOS SAN and #SANLess cluster software (www.clustersyourway.com). He more than 25 years of experience in the enterprise and high availability software industries. He holds a Bachelor of Science degree from Beloit College with graduate work in Computer Engineering and Computer Science at Boston University.