VMware Storage Blog

With the launch of vSphere 4.0, VMware introduced a new version of the ESX Server and the management server, vCenter Server. In addition vSphere enables greater resource efficiency, management control, and freedom of choice for virtual datacenter storage resources and connectivity options. A brief summary of these new storage management capabilities in vSphere 4.0 are as follows:

Virtual Disk Thin Provisioning

Virtual disk thin provisioning increases the efficiency of storage utilization for virtualization environments by dynamically allocating storage and using only the amount of underlying storage resource needed to store the contents of the virtual disk.  On average customers feedback is that they expect a reduction of 50% of their storage space. 

Improved iSCSI Software Initiator Efficiency

The new vSphere iSCSI SW initiator has been optimized for virtualization IO and provides significant improvements in CPU efficiency and throughput when compared to the earlier 3.5 version. VMware has released a new iSCSI software initiator that is far more efficient in its use of the ESX CPU cycles to drive storage IO. The entire iSCSI software initiator stack has been tuned to optimize cache affinity, enhance VMkernel TCP/IP stack, and to make better use of internal locks.

New vCenter Server Storage Enhancements

To help manage storage space in vSphere, each VM and ESX in the inventory now has its own storage tab that shows information about storage resources for those objects. The datastore can now be also managed as an object within vCenter in a manner that allows the vSphere administrator to view, group, and set permissions for each datastore. vSphere also provides a detailed view of all the components in the storage layout .These topology maps provide key information to administrators about which paths are available, as well as the grouping of objects sharing storage resources and new alerts and alarms are a key capability for to effectively managing datastores in which thin provisioned disks might create an over allocation of storage resources.

Enhanced Storage VMotion

Management of Storage VMotion is now fully integrated into vCenter Server. It offers full support to move a VM home from one datastore to another to facilitate storage migration. Some of the use case for the migration can be changing the storage protocol (FC, iSCSI or NFS) and/or change from thick to thin virtual disk format without impacting the VM.

In vSphere, Storage VMotion is also significantly more efficient because it leverages a change block tracking method that moves the VM home over to the new datastore much faster than in snapshot method used in the ESX Server release 3.5, and it no longer requires twice the CPU and memory of a give VM.

Dynamic Expansion of VMFS Volumes

VMFS Volume Grow offers a new way to increase the size of a datastore that resides on a LUN that has been recently increased in capacity, via the vSphere Client GUI without disrupting the running virtual machine. It complements the dynamic LUN expansion capability that exists in many storage array offerings today. If a LUN is increased in size, then VMFS Volume Grow enables the VMFS volume extent to dynamically increase in size as well.

 vStorage APIs for Multipathing

In vSphere, leveraging third party storage vendor multi-path software capabilities has been introduced through a modular storage architecture that allows storage partners to write a plug-in for their module to leverage. These modules can communicate with the intelligence running in the storage array to determine the best path selection, as well as leveraging parallel paths to increase performance and reliability of the IO from the ESX to the storage array. By default the native multipath driver (NMP) supplied by VMware will be used. It can be configured to support round-robin multipath as well. However, if storage vendor module is available, it can be configured to manage the connections between the ESX and the storage. There are three types of plugins, Path Selection Plug-in (PSP), Storage Array Type Plugin (SATP) and Multi-Pathing Plug-in (MPP.)

Conclusion

VMware is now providing more storage options and features that provide greater control, choice and efficiency to be leveraged in a vSphere environment. The new storage features, as well as previously existing ones (like VMFS) are grouped into an infrastructure category named vStorage. vSphere 4.0 enables the vSphere administrator to do more with less.  Extending the benefits provided by virtualization reach new levels of storage efficiency, management control and additional choices in storage connectivity. To read more on the new features in vSphere see the What’s new in vSphere - Storage paper, for detailed information on configuring see the Configuration Guide.

Authors: Paul Manning, Sr Technical Marketing Architect &

     The dynamic, flexible environment that we call VMware Infrastructure requires shared, coordinated storage between ESX servers. There are two families of storage technologies that can meet this requirement today, SAN-based block storage (e.g. Fibrechannel or iSCSI) and NAS. VMware supports both forms of storage access for our customers.

    VMFS is VMware’s technology for managing block storage. It is a clustered file system used by multiple ESX Servers to coordinate and share access to the underlying block storage. It was explicitly designed to enhance the performance and reduce the complexity of block storage as it relates to virtual infrastructure. VMFS is responsible for two broad functions in the ESX storage subsystem.

1. Structured data layout – VMFS defines the structure and layout of data on the block devices. VMFS is optimized for virtual disk storage, but as is common to most file systems, VMFS brings a file and directory structure to the on-disk data. Most importantly, VMFS handles the layout of individual vmdk files (these are the virtual disks that are eventually presented to the VMs). VMFS also has some basic layout or volume management functions – presenting and managing combinations of multiple block storage devices (LUNs) as a single VMFS volume.
2. Clustering - The second and vitally important feature of VMFS is support for sharing or clustering. VMFS is responsible for the coordination of multiple independent ESX servers safely reading and writing to the same block device. It is VMFS which handles the basic safe transfer of ownership of data from server to server during high level VI activities such as vmotion, DRS, storage vmotion, HA, etc.

    NFS is a NAS (Network Attached Storage) or file based protocol and is used to establish a client-server relationship between the ESX hosts and the NAS device. As opposed to block storage, a NAS system itself is responsible for managing the  layout and structure of the files and directories on the physical storage.  It also handles some of the aspects of shared access and provides primitives that can be used for coordinated access from multiple servers. ESX uses these primitives to provide similar shared access for VMware Infrastructure as is provided by VMFS in the block storage case.

    So which to use? The first criteria is to continue to use the type of storage infrastructure you are familiar with. If your organization uses block based storage – use VMFS.  If NAS is in use, it may make more sense to deploy VMware Infrastructure with NFS. Other aspects of storage management, such as the basic virtualization of storage on behalf of the VM or the internal structure of the virtual disk files (VMDK) are handled independently of this choice.  You get the same high level VI functionality regardless.

    For new deployments, there are the traditional storage tradeoffs. SAN or block based storage is a well understood infrastructure choice, has a great deal of existing physical management tools and may offer optimal performance. NAS-based storage has a reputation for less complexity and is in many ways easier to manage and setup than block based storage. And for some VM workloads, the performance of NAS is comparable to SAN.  Individual NAS and SAN products may offer advanced data management features that become even more valuable with Virtual Infrastructure such as data de-duplication and thin provisioning.

As with many of VMware's virtualization features, we place a great deal of emphasis on the encapsulated VM abstraction. Consistent with this philosophy, the virtual disks that are presented to virtual machines are an idealized and highly portable view of storage which is independent of the backing storage implementation. ESX handles both storage technologies in a fashion that continues to maintain this portability of the VM. With ESX and VMware Infrastructure, one can move VMs between storage technologies quite easily and now with Storage Vmotion, that portability even applies to live running workloads, offering customers the freedom to readily switch between NAS or block storage as they see fit.

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There has been some discussion lately from some of our competitors on their storage architectures or lack there of. Their boast is that VMware has a “proprietary clustered file system” that forces you to change your storage management practices while they preserve your physical storage management. They’re right, they do completely preserve the complexity of physical storage management. What they fail to mention is that this is a problem, not a solution. Physical SAN management is overly complex and a headache for most customers. And in the virtual world, the status quo is compounded! Instead of managing dedicated LUNs for every physical server, if you buy their argument you’ll be managing separate dedicated LUNs for every virtual machine! 

VMware doesn’t have a vested interested in preserving physical complexity. That’s why VMware invented VMFS and our hypervisor-based storage stack. Virtualization is all about abstracting the physical world to ease management burdens and reduce complexity. VMFS is very special purpose clustered file system that is largely transparent to our customers. It is used by VMware’s ESX Hypervisor to abstract and share LUNs used to store Virtual Machines and their Virtual Disks. 

The result? Great customer benefits, such as:

1. VMware’s instant one click provisioning, including storage. Quick, easy provisioning of a new VM, OS and application that does not require physical storage LUN provisioning.
2. Mobility/Portability. i.e Vmotion and storage Vmotion. In a virtual world, workloads should be abstracted from, not beholden to, physical storage. Just like they should be abstracted from physical servers.
3. Encapsulation and HW Independence. VMs should be entirely encapsulated from the physical world. This simple, but critically important facet of virtualization unleashes the power of virtual infrastructure. For an example, look at VMware’s new Site Recovery Manager that enables DR solutions that no longer require identical hardware (and software) configurations at each site.
4. Reduced complexity. SAN management is hard, complicated work. Why shouldn’t it be simplified?

Now is VMFS good for absolutely every use case? No, sometimes it’s important to preserve a physical LUN format for a given workload. That’s why VMware supports RDMs (Raw Disk Maps) which allows a customer to directly map an entire LUN into the guest OS while still maintaining virtual infrastructure benefits. The trade off with RDMs is more LUNs to provision and manage, but direct access from the VM to a native physical LUN.

What our competitors fail to mention is that not only does VMware support all the use cases they claim to provide, but we also bring all the benefits of virtualization to the entire data center, storage included. And that’s something worth touting!

Welcome to the VMware Storage Blog, a blog dedicated to all aspects of storage in the virtual environment.
We get a lot of questions about Storage Architecture in VMware Virtual Infrastructure. It is a complex topic with many options and design trade-offs to consider. In this blog we will attempt to demystify the topic. Please let us know how we are doing! Thanks.