Handbook
PERFORMANCE
SCALABILITY
HYPERVISOR-RELATED FEATURES AND STORAGE MANAGEMENT
DATA PROTECTION
VIRTUAL SERVER STORAGE FEATURE CHECKLIST HYPERVISOR-AWARE STORAGE PRODUCT CATEGORIES VIR TU ALIZA TION CL OUD APPLIC ATION DEVEL OPMENT HEAL TH IT NETW ORKING ST ORA GE ARCHITE C TURE D AT A CENTER MANA GEMENT BI/APPLIC ATIONS DIS A STER RE CO VER Y/COMPLIANCE SE CURITY
Buyer’s Checklist to
Purpose-Built Storage
for Virtual Servers
When virtual servers began to proliferate, storage systems often
became the bottleneck; but storage built specifically to support
virtual servers erases many of those problems.
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories PERFORMANCE
Buyer’s Checklist to Purpose-Built
Storage for Virtual Servers
When virtual server technology gradually became dominant in most data centers, it soon became apparent that many traditional storage systems weren’t up to the task of serving the new virtualized server environment. Perfor-mance issues cropped up almost immediately as SAN and network-attached storage (NAS) systems struggled to deliver the IOPS and throughput virtual machines (VMs) required. The situation even spawned its own terminol-ogy to describe the new bottlenecks caused
by VMs with terms such as I/O blender effect
and boot storm entering the enterprise storage lexicon.
Storage vendors reacted fairly quickly, as did hypervisor vendors, to help address some of these issues. But the new virtual server model also helped to create a new category of storage
array: hypervisor-aware storage systems. These
systems are built from the ground up to provide storage for virtual environments, with special emphasis on performance and agility. Along the way, many of these systems have broken away from the traditional models and methods of configuring, provisioning and managing stor- age, with a decidedly hypervisor-specific ap-proach to these tasks. In this Buyer’s Checklist, we describe how these storage systems differ from traditional arrays, provide insights into some of their unique features and offer guidance on evaluat-ing, purchasing and deploying these storage systems. PERFORMANCE As virtual servers are introduced into the data center and quickly proliferate, performance is- sues with storage systems designed for physi-cal server requirements start to crop up. While physical servers maintain a 1:1 relationship to storage with fairly predictable performance
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories characteristics and a low degree of concurrency, virtualized servers throw that “simple world” into a frenzy of physical servers hosting VMs, and VMs running a mix of applications with varying workloads. A high degree of concur- rency where VMs and applications are in con-tinuous pursuit of resources, including storage, pushes storage systems to their performance limits and impacts the ability of storage admin-istrators to correlate applications to underlying physical storage resources and components. To make matters worse, advanced storage techniques such as thin provisioning aggravate the problem by enabling multiple VMs to share storage blocks, requiring the storage system to support an even higher number of IOPS. Addressing these performance challenges ef-fectively is one of the value propositions of hypervisor-aware storage systems, which em-ploy various techniques to achieve acceptable performance. n Flash. Without question, solid-state storage is one of the key components that enable stor-age systems to better support the performance requirements of virtualized environments. While NAND flash supports tens of thousands of IOPS, a single hard disk drive is limited to a few hundred IOPS; for disk-based arrays to scale IOPS, they depend on the paralleliza- tion of a large of number of disk drives, strip-ing data across them, so that many disks are at work at any given time when data is served. NAND flash is superior to physical disk in its ability to support a large number of IOPS in al-most all aspects, including cost and complexity. Since the number of IOPS is typically more relevant than throughput for VM storage—but the type of applications on the VMs can affect this—employing solid-state storage reaps im-mediate performance benefits. A case in point that perfectly illustrates the relevance of IOPS is the well-known boot storm that occurs when many VMs that share the same physical blocks of the underlying storage all boot at the same time and spike the required IOPS. Flash storage is one of the most effective ways of addressing this scenario. That solid-state storage should be a
component of hypervisor-aware stor-age is undisputed, but where it’s deployed
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories PERFORMANCE hypervisor-aware storage systems. Substituting mechanical disk drives with solid-state drives (SSDs) is the easiest way of flash-enabling a storage array; the drawback of SSDs is that only data that resides on the SSDs benefits from it. Some hypervisor-aware storage systems deploy flash as cache, with the advantage that all apps benefit from it. The amount of flash—and whether it’s used for reads only, or for reads and writes—is an important consideration. Flash can be de-ployed on the server, usually in the form of PCI Express cards; its proximity to the CPU and server memory, and reducing the number of transactions that have to traverse to the stor- age system through a relatively performance-constrained interface, makes flash on the server the best performing flash deployment option.
n Storage tiering. While the number of IOPS a
storage system can support is very important, the cost of NAND flash is still significantly higher than that of physical disk. Since IOPS requirements fluctuate, a mechanism to sup-port spikes when needed but that’s also able to take advantage of less-expensive mechanical disks where appropriate, can help keep the cost of hypervisor-aware storage systems down. This mechanism is available in the form of storage tiering, where mechanical disks and solid-state storage complement each other. Two schools of thought exist on how to keep active data most effectively in NAND flash. One group of vendors champions policy-based data movement, while another espouses the use of NAND flash as cache that sits in front of mechanical disks. The latter is usually the less complex approach since NAND flash simply becomes another cache that sits between the DRAM cache and disk drives, relying on proven caching algorithms to keep active data in the appropriate tier.
n Quality of Service (QoS).
The ability to pri- oritize data by application and data type en-ables storage administrators to ensure that critical applications aren’t bogged down by less
critical ones. The support of QoS is a critical
element of a hypervisor-aware storage system, and it should be considered a must-have crite- rion on anyone’s evaluation list. QoS is the sil-ver bullet that enables putting any type of data
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories and workload on a shared storage system with the needed safeguard to protect critical appli-cations, with QoS as the arbiter to keep lower priority data and applications at bay. SCALABILITY A clear understanding of the scalability limits of the hypervisor-aware storage system you’re about to acquire is essential to prevent unpleas-ant surprises. In a product evaluation, questions about the target market, the ability to scale be-yond a single box and the largest deployments in which the system is in use help identify if the product meets your scalability require-ments. For instance, a product targeted for the small and medium-sized business market is likely not going to be able to scale to enterprise requirements. Capabilities that are usually not found in storage systems, such as the ability to use the storage system to also run VMs, need to be analyzed for their impact on scalability. The benefits of rapid deployment and simplicity of a converged system is in some products offset by limited scalability. Last but not least, the ability to scale without the need for data migration is indispensable, especially as storage systems for VMs can grow fairly large. HYPERVISOR-RELATED FEATURES AND STORAGE MANAGEMENT
A key aspect of evaluating hypervisor-aware storage is how the storage system supports
and integrates with hypervisors. Most storage
systems support VMware vSphere and Micro-soft Hyper-V; other hypervisors, such as Citrix XenServer and Red Hat, are usually lower pri-ority and some storage systems don’t support them at all. For supported hypervisors, you need to de- termine the level of integration and the sup-ported APIs. In the case of VMware, you’ll want to know if the storage system supports the
The ability to scale without the need for data migration is indispensable,
especially as storage systems for VMs can grow fairly large.
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories HYPERVISOR- RELATED FEATURES VMware vStorage APIs for Array Integration (VAAI) that enable offloading of storage tasks, such as copying and moving data and thin pro-visioning, from the VMware hypervisor to the storage array. You’ll also want to know to what degree the VMware vStorage APIs for Storage Awareness (VASA) are supported. VASA en-ables storage arrays to integrate with VMware vCenter for management functionality, giving vSphere administrators insight into storage ca-pabilities via plug-ins (or “providers”) through which vCenter can receive information about capabilities, health status, configuration and capacity from the underlying array, and display it in the vCenter user interface. In the case of Microsoft Hyper-V, you’ll need
D
SPECIAL FACTORS: VM-SPECIFIC STORAGEwithoutquestion, startups are pioneering storage architectures and features that are intended to better support virtual server environments. When evaluating hypervisor-aware storage, weighing the risk inherent to a startup and the benefits of its products is an important exercise. You need to consider if it will be around for the long run, if it’s able to offer adequate support, and whether the product is mature and stable. It may be prudent to have a plan B if the startup vanishes or the product doesn’t live up to its promises. These are important issues you need to address before making a buying decision.
Some hypervisor-aware storage only supports virtual servers and will not work with physical servers. Others only support a specific hypervisor, such as VMware vSphere or Microsoft Hyper-V. Clearly, understanding what’s supported is critical to protect your investment.
Discuss roadmaps during your evaluation. Since hypervisor-aware storage is still evolving, understanding future features is important. What hypervisors are on the roadmap? What hypervisor application programming interfaces are planned? Make sure the roadmap aligns with your business requirements.
Validate storage features that have become standard in storage arrays, from thin provisioning, snapshots and replication to compression, deduplication and cloud storage integration. Hypervisor-aware products may offer a newfangled way of interacting with hypervisors, but they may not be up to speed with standard array features.n
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories to know if the array supports Windows Server 2012 Offloaded Data Transfer (ODX) to enable offloading of copy and move operations to stor-age arrays. It’s also important to ask if the array supports the Storage Management Initiative Specification (SMI-S) or Storage Management Packs to enable managing storage from within System Center Virtual Machine Manager 2012. One of the challenges of traditional storage systems in virtualized server environments has been the level at which storage is provisioned and managed. Traditionally, storage has been provisioned and managed at a LUN level. A LUN is usually assigned to a physical server, and storage from the LUN is then assigned to VMs. Without further integration between the underlying storage array and the hypervi- sor, it can be challenging to correlate virtual-ized resources to the physical storage array and components, such as disks and controllers. Some hypervisor-aware storage system vendors have changed the storage architecture to pro-vision and manage storage at a VM level, and others have complemented traditional stor-age systems with auxiliary tools that provide that insight. The ability to correlate applica- tions on VMs to the underlying physical stor-age, providing visibility to the full data path, is an indispensable ability any hypervisor-aware storage system should have. DATA PROTECTION The simplicity of spawning new VMs that inevitably result in a greater number of serv-ers, combined with the abstraction inherent to virtualization, makes data protection of virtu-alized servers a more challenging task. Back-ing up VMs via backup agents that run on the VMs is problematic because of the overhead and impact on performance. Backing up the physical host can be problematic as well unless the VMs it hosts and the applications within each VM are backed up in a consistent state; (Continued on page 9)
Backing up VMs via backup
agents that run on the VMs is
problematic because of the over-
head and impact on performance.
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories CHECKLIST
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VIRTUAL SERVER STORAGE FEATURE CHECKLISTFEATURE Performance Scalability Hypervisor and application programming interface (API) support Ability to manage storage at a virtual machine (VM) level Convergence factor Data protection capabilities
WHY IT’S IMPORTANT
Needs to support the IOPS and throughput requirements of virtualized servers Determines to what degree a storage system can scale
• Determines how widely a storage system can be used
• APIs enable integration of the hypervisor with the storage system
• Enables visibility of the full data path from the VM to the spindle
• Eases identifying and remediating storage-related problems
Combining storage and VMs in a single system simplifies management and lowers cost
Leverage data protection features of storage system to back up virtualized servers
OPTIONS
• Solid-state storage
• Tiering solid-state storage and disk drives
• Quality of Service to prioritize critical applications Scalability options are product specific:
• Scaling vertically by adding processing, memory and disk resource
• Scaling horizontally by adding nodes
• APIs that enable offloading of storage tasks to the storage system
• Management APIs that allow the storage system to be managed from within the hypervisor manage-ment console
• Provisioning of storage at the VM level inherently results in managing storage at a VM level (ideal)
• Provision storage at LUN level and use auxiliary methods, such as storage analytics, to relate VMs and applications within the VM to physical storage resources
• Systems that combine storage and VMs
• Turnkey systems optimized for virtualized server environments
• Snapshots and replication
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories this requires data in memory to be flushed to disk to ensure all data is backed up and restores can be performed in an application-consistent manner. Hypervisors provide APIs to aid in data protection: VMware has its vStorage API for Data Protection (VADP) and Micro-soft’s Volume Shadow Copy Service (VSS) enables application-consistent snapshots of VSS-enabled applications. Hypervisor-aware storage systems can play an essential role in simplifying this data protection challenge via techniques such as snapshots, replication and continuous data protection. HYPERVISOR-AWARE STORAGE PRODUCT CATEGORIES Virtualization is in vogue and all storage sys-tems claim to be hypervisor-aware, but some products are more hypervisor-aware than oth- ers. Here’s a product grouping of hypervisor-aware storage systems.
n Systems that manage storage at the VM level.
These products provision, manage and monitor storage at the VM level. They offer out-of-box, full-data-path transparency from application to spindle. They are currently only available from promising startups. Traditional storage vendors try to address this niche via add-ons, such as storage analytics that provide this degree of insight.
n Converged systems that combine storage and
VMs. Products in this category provide both storage services and the ability to run VMs in a single system. Their value proposition is to maximize system utilization and simplify man-agement. The ability to scale and the impact of VMs on storage performance should be your main concern when evaluating a converged sys- tem. Again, products in this category are cur-rently only available from startups.
n All-flash arrays. Products in this category
forgo mechanical disks and only use solid-state storage to maximize performance. They’re tar-geted at applications that require a very high IOPS. They’re expensive, and some products in this category lack storage features that are by now standard in enterprise arrays.
Home Performance Scalability Hypervisor-Related Features and Storage Management Data Protection Virtual Server Storage Feature Checklist Hypervisor-Aware Storage Product Categories PRODUCT CATEGORIES
n Fully converged storage systems.
Fully con- verged systems are integrated turnkey plat-forms in which servers, storage, network connectivity and software are built into a single offering that’s sold and supported by one vendor. These turnkey systems are available from traditional storage vendors and smaller vendors for both VMware and Hyper-V hypervisors.
n Traditional storage systems. The primary
competitors of so-called hypervisor-aware storage systems, which are explicitly targeted for use with virtualized servers, are tradi-tional storage arrays. Since almost all arrays have added capabilities that benefit virtualized servers, the gap between so-called hypervisor-aware storage systems and traditional storage systems may be small in some cases, so tradi-tional storage systems should be part of your product evaluation. n
JACOB N. GSOEDL is a freelance writer and a corporate
director for business systems. He can be reached at
Buyer’s Checklist to Purpose-Built Storage for Virtual Servers is a SearchVirtualStorage.com e-publication.
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