VMware virtual servers offer advanced shared storage options

Discover why VMware virtual servers offer more advanced options, including new APIs, for shared storage systems than Microsoft Hyper-V and Citrix XenServer.

Citrix Systems Inc., Microsoft Corp. and VMware Inc. all present IT shops with a variety of options to provision and manage the shared storage systems that are linked to their virtual server technology.

Not surprisingly, VMware, the vendor with the most mature product in the market, offers the most advanced support for block- and file-based networked storage alternatives and makes available application programming interfaces (APIs) data storage vendors can use to ensure their systems will work smoothly with its virtual server software, noted Marc Staimer, president at Dragon Slayer Consulting in Beaverton, Ore.

In this podcast interview, Staimer outlines VMware virtual servers, what VMware has done to improve the way its products work with storage, contrasts where Microsoft Hyper-V and Citrix XenServer stand in comparison, and offers up advice on choosing the right data storage option for your virtual server environment. You can read the transcript below or download the MP3.

Listen to the VMware virtual servers Q&A.

SearchStorage.com: VMware has the most mature virtual server technology in the market. What has VMware done over the years to make the configuration, allocation and management of storage easier?

Staimer: VMware isn't just the most mature of the hypervisors in the market; it's actually the most advanced, especially when it comes to storage. They do things with storage that nobody else does at this point, including things such as virtualizing the I/O for block-level storage. They work with all the different SAN technologies, whether you're talking iSCSI, Fibre Channel or FCoE [Fibre Channel over Ethernet]. They work with NAS, file-based storage, specifically NFS, because they've built it into the kernel, so any virtual machine [VM] can use NFS.

It's incredibly easy at that point, and they've improved the performance they provide for NFS and iSCSI so it's fairly much on par with Fibre Channel at this point. They do a number of interesting things with storage; they have storage APIs that allow their system to manage other people's storage systems and vice versa. They have the ability to provide for disaster recovery using something called Site Recovery Manager, or SRM. Now all of this requires a storage vendor to be self-certified with VMware in these different functions. But they do a good job of integrating with storage better than I've seen from anyone else.

SearchStorage.com: Although VMware has been the leader in virtual server technology for quite some time, Microsoft's Hyper-V is starting to gain traction. Are there any major distinctions in the way one would provision and manage storage in a VMware environment vs. a Microsoft virtual server environment?

Staimer: Actually, there are a quite a few. One of the key ones that I look at is how … you handle different VMs going to the same storage. Now they both virtualize in block storage. So, what happens when you have different VMs within that physical machine accessing the same disks at the same time? As far as the storage system is concerned, this is one server, one application. It's handling it on a first-in, first-out [basis], so that you could have a mission-critical application waiting for someone to copy an MP3. Not exactly a great idea. The storage system can't distinguish between VMs. Well, VMware allows you to distinguish between VMs. It allows you to set priorities based on latency or IOPS. It allows you to reprioritize the I/O to a specific VM as a result of those policies. You don't get that with Hyper-V.

Hyper-V is a good product. It's coming along. It's trying to get features that VMware currently offers. One way to bring Hyper-V closer to some of the functionality you get directly out of VMware is to partner with some third-party products like Sanbolic. [It's] a clustered file system that takes Hyper-V and brings it closer to the functionality you would expect out of VMware.

SearchStorage.com: Citrix's XenServer presents yet another option for virtualizing servers. Are there any special considerations for storage in a XenServer environment?

Staimer: It's a fine product. It works fine with storage. There isn't anything really outstandingly unique about it. It works with NFS. It also has an NFS client built into its kernel. And again, the easiest storage with either VMware or XenServer is NFS. But it doesn't do much in quality of service. It's trailing when it comes to disaster recovery functionality, storage migration functionality. It's got a long ways to go, just like Microsoft. But, for the money, you get a pretty good product.

SearchStorage.com: What's the major piece of advice you'd offer to IT shops selecting networked storage for their virtual server environments?

Staimer: Go with the storage that best meets the skills you have in your IT center and meets [the] needs of your applications. For me, I'd probably go with NFS. For other people, it will depend. I could recommend iSCSI or Fibre Channel or FCoE or even CIFS. It just depends. I'd have to look at each shop differently as to what their needs are, what their skills are, what they have and what they're used to.

In some cases, if they have no SAN experience, no NAS experience, no NFS and they really don't want to go that route, then I would tell them to go with a virtual storage appliance. On the block side, you have people like VM6, Seanodes, [Hewlett-Packard's] LeftHand Networks, DataCore Software and FalconStor, which can create a virtual SAN to provide you [with] the ability to use those advanced features, but you don't really have to implement a SAN. If you need a virtual NAS environment, you could go with someone like a Nasuni or, if you're in a pure Hyper-V environment, somebody like a Sanbolic, so that you get the functionality, the ability to use shared storage without having to implement shared storage.

SearchStorage.com: Are there any scenarios in which it might be advantageous to use direct-attached storage (DAS) in a virtual server environment?

Staimer: Sure. If you only have one physical machine that you're running your hypervisor on, direct-attached storage is just fine. On the other hand, if you want to use any of those advanced features, like VMotion in VMware or Storage VMotion or SRM or DRS -- I mean, these are really great functional features that reduce your administration, that do things online so you don't have to schedule downtime -- you're going to need some kind of shared storage. DAS kind of limits that.

Now if you can take your DAS and make it appear like a SAN virtually, as I mentioned before, then you can use DAS, using the Seanodes, the VM6s, the LeftHands, the DataCores, the FalconStors, the Nasunis, the Sanbolics, so that it looks like you have shared storage when you don't. So, that's the best time to use DAS.

This was first published in March 2011

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