Datakeeper Archives - Page 7 of 8 - SIOS SANless clusters

DHCP Cluster Without Shared Storage And/Or Across Data Centers

January 22, 2018 by Jason Aw Leave a Comment

Look for a Step-by-Step article on how to configure a DHCP across data centers and/or without shared storage in the very near future using Windows Server Failover Clustering and SteelEye DataKeeper Cluster Edition. In the meantime, check out this video that demonstrates a DHCP cluster that uses a replicated DHCP database instead of a shared disk in the cluster.

Reproduced with permission from https://clusteringformeremortals.com/2009/11/23/dhcp-cluster-without-shared-storage-andor-across-data-centers/

Hyper-V Live Migration Across Data Centers

January 22, 2018 by Jason Aw Leave a Comment

There has recently been a lot of press, about executing virtual machines live migrations across long-distanced data centers, that herald VMware’s limited support for vMotion across Data Centers, or “long-distance vMotion” as I have seen it called. The details of the solution can be found on Cisco’s website here. While I think that is just great, I’d like to remind people that Microsoft Hyper-V has this same functionality today and has a lot less requirements and restrictions than VMware’s long-distance vMotion.

Where VMware has VMwareHA, vMotion and Site Recovery Manager (SRM) to take care of virtual machine availability, Microsoft provides the same functionality with Windows Server Failover Clustering and in fact in some cases goes beyond what VMware can provide in terms of virtual machine availability as I described in a previous post.

What I’d like to focus on today is Microsoft’s competitive offering to “long-distance vMotion”. To achieve the same functionality in Hyper-V, you simply deploy a multi-site Hyper-V cluster using Windows Server Failover Clustering and your favorite host or storage based replication solution that is certified to work in a Windows Server 2008 multi-site cluster. By doing this, you can use your existing network infrastructure and your existing storage infrastructure to do Live Migrations across data centers. As far as requirements, they really are the same as any multi-site cluster, except I would recommend that you span your subnets to avoid client reconnection issues that occur when moving a virtual machine to a new subnet, as the clients could cache to old IP address until the TTL expires.

A demonstration video of Live Migration across data centers using Windows Server 2008 R2 Hyper-V and SteelEye DataKeeper Cluster Edition can be seen here.

Reproduced with permission from https://clusteringformeremortals.com/2009/09/17/hyper-v-live-migration-across-data-centers/

Remove The Weakest Link, Ensure High Availability Cluster Configuration

January 21, 2018 by Jason Aw Leave a Comment

Build A High Availability Cluster Configuration

When we build a High Availability Cluster Configuration, your application availability is only as good as its weakest link. What this means is that if you bought great servers with redundant everything (CPU, fans, power, RAID, RAM, etc) and a super deluxe SAN with multi-path connectivity. Coupled with multiple SAN switches and clustered your application with your favorite clustering software. You probably have a very reliable application – right? Well, not necessarily. Are the servers plugged into the same UPS? Are they on the same network switch? Are they cooled by the same AC unit? Are they in the same building? Is your SAN truly reliable? Any one of these issues among others is a single point of failure in a High Availability Cluster Configuration.

Seek And Remove The Weakest Link in Cluster Configuration

Of course, you have to know when “good enough” is “good enough”. Your budget and your SLAs will help decide what exactly is good enough. However, one area where I am concerned that people may be skimping is in the area of storage. With the advent of cheap or free iSCSI target software solutions, I am seeing some people recommend that you just throw some iSCSI target software on a spare server and voilà – instant shared storage.

Mind you I’m not talking about OEM iSCSI solutions that have built in failover technology and/or other availability features; or even storage virtualization solutions such as FalconStor. I’m talking about the guy who has a server running Windows Server 2008 that he has loaded up with storage and wants to turn it into an iSCSI target. This is great in a lab. But if you are serious about HA, you should think again. Even Microsoft only provides their iSCSI target software to qualified OEM builders experienced in delivering enterprise class storage arrays.

What You Are Actually Getting?

First of all, this is Windows. Not some hardened OS built to only serve storage. It will require maintenance, security updates, hardware fixes, etc. It basically has the same reliability as the application server you are trying to protect. Does it make sense to cluster your application servers. Yet use the same class of server and OS to host your storage? You basically have moved your single point of failure away from your application server and moved it to your storage server. It’s not a smart move as far as I am concerned.

Some of the Enterprise Class iSCSI target software includes synchronous and/or asynchronous replication software and snapshot capabilities. This functionality certainly helps in terms of your recovery point objective (RPO). Although it won’t help your recovery time objective (RTO) unless the failover is automatic and seamless to your clustering software. Let’s say the primary iSCSI storage array fails in the middle of the night. Who is going to be there to activate the replicated copy? You may be down for quite some time before you even realize there is a problem. Again, this may be “good enough”; you just need to be aware of what you are signing up for. Is that the High Availability Cluster Configuration you’re seeking?

SIOS DataKeeper

One thing you can do to improve the reliability of your iSCSI target server is to use a replication product such as SteelEye DataKeeper Cluster Edition to eliminate the single point of failure. Let me illustrate.

Figure 1 – Typical Shared Storage Configuration. In the event that the iSCSI target becomes unavailable, all the nodes go offline.

If we take the same configuration shown above and add a hot standby iSCSI target using SteelEye DataKeeper Cluster Edition to do replication AND automatic failover, you have just given you iSCSI target solution a whole new level of availability. That solution would look very much like this.

DataKeeper Cluster Edition - High Availability Cluster Configuration — Figure 2 – In this scenario, DataKeeper Cluster Edition is replicating the iSCSI attached volume on the active node to the iSCSI attached volume on the passive node, which is connected to an entirely different iSCSI target server.

The key difference in the solution which utilizes SteelEye DataKeeper Cluster Edition vs. replication solutions provide by some iSCSI target vendors is in the integration with WSFC. The question to ask of your iSCSI solution vendor is this…

What happens if I pull the power cord on the active iSCSI target server?

If the recovery process is a manual procedure, it is not a true HA solution. But what if it is automatic and completely integrated with WSFC? Then you have a much higher level of availability and have eliminated the iSCSI array as a single point of failure.

Chat with us to also achieve High Availability Cluster Configuration

Reproduced with permission from Clusteringformortals.

Steeleye Datakeeper Cluster Edition Wins Windows It Pro Best High Availability/Disaster Recovery Awards

January 20, 2018 by Jason Aw Leave a Comment

I am pleased to announce that Windows IT Pro has awarded SteelEye DataKeeper Cluster Edition the Best High Availability and Disaster Recovery Product in two categories; Community Choice Gold Award and Editors’ Best Silver Award.

I am really proud to be a part of the SteelEye DataKeeper team and I appreciate all of the Windows IT Pro community that voted for us in the Community Choice award!

Reproduced with permission from https://clusteringformeremortals.com/2009/11/20/steeleye-datakeeper-cluster-edition-wins-windows-it-pro-best-high-availabilitydisaster-recovery-awards/

How Can Asynchronous Replication Be Used In A Multi-Site Cluster? Isn’t The Data Out Of Sync?

January 18, 2018 by Jason Aw Leave a Comment

How Can Asynchronous Replication Be Used In A Multi-Site Cluster? Isn’t The Data Out Of Sync?

I have been asked this question more than a few times, so I thought I would answer it in my first blog post. The basic answer is yes, you can lose data in an unexpected failure when using asynchronous replication in a multi-site cluster. In an ideal world, every company would have a dark fiber connection to their DR site and use synchronous replication with their multi-site cluster, eliminating the possibility of data loss. However, the reality is that in many cases, the WAN connectivity to the DR site has too much latency to support synchronous replication. In such cases, asynchronous replication is an excellent alternative.

What Are My Options?

There are more than a few options when choosing an asynchronous replication solution to use with your WSFC multi-site cluster. This includes array based solutions from companies like EMC, IBM, HP, etc. and host based solutions, like the one that is near and dear to me, “SteelEye DataKeeper Cluster Edition“. Since I know DataKeeper best, I will explain how this all works from DataKeeper’s prospective.

What About SteelEye DataKeeper?

When using SteelEye DataKeeper and asynchronous replication, we allow a certain number of writes to be stored in the async queue. The number of writes which can be queued is determined by the “high water mark”. This is an adjustable value used by DataKeeper to determine how much data can be in the queue before the mirror state is changed from “mirroring” to “paused”. A “paused” state is also entered anytime there is a communication failure between the secondary and primary server. While in a paused state, automatic failover in a multi-site cluster is disabled, limiting the amount of data that can be lost in an unexpected failure. If the original data set is deemed “lost forever”, then the remaining data on the target server can be manually unlocked and the cluster node can then be brought into service.

While in the “paused” state, DataKeeper allows the async queue to drain until we reach the “low water mark”, at which point the mirror enters a “resync” state until all of the data is once again is in sync. At that point, the mirror is once again in the “mirroring” state and automatic failover is once again enabled.

As long as your WAN link is not saturated or broken, you should never see more than a few writes at any given time in this async queue. In an unexpected failure (think pulled power cord) you will lose any write that is in the async queue. This is the trade off you make when you want the awesome recovery point objective (RPO) and recovery time objective (RTO) which you achieve with a multi-site cluster, but your WAN link has too much latency to effectively support synchronous replication.

Try The SteelEye DataKeeper

Take time to monitor the DataKeeper Async Queue via the Windows Performance Logs and Alerts. I think you will be pleasantly surprised to find that most of the time the async queue is empty due to the efficiency of the DataKeeper replication engine. Even in times of heavy writes, the async queue seldom grows very large and always drains almost immediately. So the amount of data that is at risk at any given time is minimal. Compared to the alternative in a disaster to restore from last night’s backup, the number of writes you could lose in an unexpected failure using asynchronous replication is minimal!

Of course, there are some instances where even losing a single write is not tolerable. In those cases, it is recommended to use SteelEye DataKeeper’s synchronous replication option across a high-speed, low latency LAN or WAN connection.

Reproduced with permission from Clusteringformeremortals.com