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Network attached storage in a virtualised environment
In a virtualised environment, network attached storage appliances can serve as a swap space to move virtual machines between servers, act as a backup medium, or play the role of central repository for all virtual disk images.
NAS versus SAN for data center virtualisation storage
There are two major approaches to network storage: network attached storage (NAS) and storage area network (SAN). They vary in both network architecture and how each presents itself to the network client. NAS devices leverage the existing IP network and deliver file-layer access. NAS appliances are optimised for sharing files across the network because they are nearly identical to a file server. SAN technologies, including Fibre Channel (FC) and iSCSI, deliver block-layer access, forgoing the file system abstractions and appearing to the client as essentially an unformatted hard disk. FC operates on a dedicated network, requiring its own FC switch and host bus adapters in each server. An emerging standard, Fibre Channel over Ethernet (FCoE), collapses the storage and IP network onto a single converged switch, but still requires a specialised converged networking adapter in each server. SAN solutions have an advantage over NAS devices in terms of performance, but at a cost of some contention issues.
Understanding failover and failback
By definition, failover is the capability to switch over to a redundant or standby server, system or network upon the failure or termination of an existing asset. This should occur without any kind of human intervention or warning. This contrasts with switch-over, where you’re dynamically making a transition from one environment to another.
Failback is the process of restoring a system or another asset that’s in a failover state back to its original state. The assumption is that you’re able to bring it back to the state of operation before the disruption.
With a virtualised environment, you can failover to the environment which exists in real time, and it’s very easy to failback to the original mode because you can maintain images of your previous environments.What’s nice about this is that it speeds up your recovery time and it’s possible to do testing on an actual system without adversely affecting your actual production environment. You can then turn it on or off as quickly as you’d like, so virtualisation really helps in the area of testing.
The benefits of using virtualisation
Virtualisation can provide some clear benefits for disaster recovery planning; it can help save money, time and effort, and make the often daunting task of designing and implementing a disaster recovery plan easier.
Additional benefits of using virtualisation as part of your disaster recovery strategy include:
- Fewer physical servers needed at a disaster recovery site reduces onetime and ongoing costs, and results in less idle hardware.
- Lower cost virtual machine (VM)-level replication is storage independent and doesn’t require expensive storage arrays.
- Hardware independence allows for more hardware options without compatibility issues
- Encapsulation turns a VM into a single portable file for easier transport and deployment.
- Snapshots provide an effective method for backup of virtual machines.
- Automated failover and easier testing.
- Easier server deployment; scripting can be used to help automate many configuration and operational tasks.
UK users lack off-site backup and DR
More than one-third (36%) of UK businesses have no off-site backup and disaster recovery strategy, and more than two-thirds (71%) do not back up or do not know if they back up their virtual servers as often as their physical servers.
That's according to backup product vendor Acronis, which has launched its Global Disaster Recovery Index to survey 3,000 SME IT managers about the level of confidence they have in their backup and recovery operations.
The survey found that greatest challenge for the majority (67%) of UK IT managers is moving data between physical, virtual and cloud environments. The average UK business currently uses at least two to three separate backup solutions, with one-third (35%) using four or more to manage their different environments and further complicating DR.
Those who have no off-site backup and DR strategy in place cite lack of budget and resources as the primary reasons why it is not more of a priority. But, as a proportion of all IT spend, the UK spends slightly less (10%) on backup and DR than those that came out with the best overall results, Germany (13%) and the Netherlands (14%).
The poor results for UK businesses on backing up virtual servers came despite an expected 25%increase in the deployment of virtual production servers in 2011.More than half (56%) of companies surveyed worldwide use different solutions for both their physical and virtual backups.
FCoE vs iSCSI? How about the one that’s ready?
Vendors can push Fibre Channel over Ethernet (FCoE) all they want, but the technology is simply not ready for deployment, argues Stephen Foskett, Gestalt IT community organiser. But iSCSI is another story.
“I am not a big fan of FCoE yet. The data centre bridging (DCB) extensions are coming … but we don’t yet have an end-to-end FCoE solution.We don’t have the DCB components standardised yet,” Foskett said.
What does Foskett think it will take to make FCoE work?
“It’ll take a complete end-to-end network. I understand the incremental approach is probably now what most people are going to do. It’s not like they’re going to forklift everything and get a new storage array and get a new greenfield system, but right now you can’t do that,” Foskett said.
iSCSI, on the other hand, works over 10 Gigabit Ethernet today and lends itself to a total solution. So why aren’t vendors selling it?
“iSCSI doesn’t give vendors a unique point of entry. They can’t say we’ve got iSCSI, so that makes us exceptional. But with FCoE they can say, ‘We are the masters of Fibre Channel’ or ‘We are the masters of Ethernet, so you can trust us.’ iSCSI works too well for anybody to have a competitive advantage,” Foskett said.
This was first published in February 2011