(866) 683-8844 Phone
(609) 683-9664 Fax
338 Wall Street
Princeton, NJ 08540
(Directions)
This
page is
printer friendly.
TechNote:
Storage Virtualization
Virtual Servers with Virtualized Storage
Virtual machines make efficient use of the underlying physical computing resources by enabling multiple production and development environments to co-exist on a single machine. In the enterprise, they provide flexible server resource management and high-availability capabilities.
VMware and DataCore Software
VMware®, (www.vmware.com) now owned by EMC, provides a virtual machine environment that runs on Intel x86 platforms, supporting workstations and servers running Windows or Linux as the host OS, through the enterprise platforms that embed the ESX OS host kernel.
DataCore Software's (www.datacore.com) SANsymphony™ & SANmelody™ products offer the ability to consolidate and manage any heterogeneous collection of SAN storage resources and provide automated storage management and provisioning in a hardware-independent and application-independent fashion.
Virtual Servers and Virtual Storage
Currently, the fastest growing type of implementation for DataCore Software's SANsymphony™ and SANmelody™ storage virtualization software is in environments where virtual servers are implemented using VMware®.
Typically, these involve the use of FC connectivity to GSX or ESX VMware platforms, along with iSCSI connectivity to dedicated application servers where the performance capabilities of iSCSI are suitable. Since the DataCore environment is independent of the choice of storage, the underlying storage arrays in these implementations cover a wide range of manufacturers and models.
All of the advanced storage management features such as automated capacity provisioning, snapshots, asynchronous mirroring over IP, and high-availability alternate pathing with synchronous mirroring, are being used. In addition, the advanced capabilities of VMware such as VMotion are also being used.
Using both Virtual Server (VMware) and Storage Virtualization (DataCore) software technologies will:
- Increase both storage and server CPU utilization rates up to 80% or more
- Reduce provisioning times for storage and CPU resources for new applications from days to minutes
- Accelerate response times for change requests.
- Eliminate disruptions for upgrades and hardware maintenance
- Support a variety of high-availability architectures
- Eliminate server and storage hardware vendor "lock-in"
Certification of VMware with DataCore's Storage Virtualization
Today, VMware has "certified" a limited number of storage array products for use with their software. DataCore's Storage Virtualization products are software, not hardware, and DataCore has certified VMware to work with all DataCore functions including high-availability, automated provisioning and snapshots.
Storage Connectivity with VMware - Fibre-Channel or iSCSI?
The primary driver for using VMware is achieving an economical CPU resource utilization. Typically, stand-alone application servers only use 10% of the CPU resources. Combining logically separated applications on a single server platform increases CPU utilization to 80%, simplifies connectivity, reduces hardware costs, and facilitates server management tasks.
Conversely, shared access to a single I/O resource reduces the theoretical storage connectivity performance available to any individual virtual machine partition, and increases the cost of any connection failure if an alternate pathing capability is not available to the multiple applications hosted on the physical platform.
The choice of FC versus iSCSI needs to be carefully evaluated in the context of the application performance and availability needs.
FC and VMware
VMware supports virtual machines of several flavors (Win2K, Solaris, Linux, NetWare, etc.) on the same hardware node with the ability to boot any of those VMware partitions off of a drive presented over a FC SAN. Multi-pathing support from a VMware platform is also possible.
FC connectivity is smoothly scalable from legacy 1 Gbit FC, through the new 4 Gbit FC infrastructures. At the hardware level, the costs and complexities for FC are today substantially reduced from historical levels. There are a number of cost-effective FC fabric switch solutions available from several manufacturers that provide easy manageability.
Because a single physical FC HBA can support several virtual machines in a VMware implementation, the economics are more favorable with FC in a VM world than they are with discrete machines for each application.
VMware ESX and GSX support FC now and, importantly, ESX provides native multi-pathing support for high-availability. The inherently greater performance and bandwidth scalability of FC combine to alleviate I/O performance concerns with multiple partitions sharing a single resource.
iSCSI and VMware
Any VMware partition that implements a conforming iSCSI initiator (such as the Windows iSCSI initiator) on the partition, can share an IP connection for iSCSI services just as it does a FC connection. For example, Windows VM partitions can mount data volumes over iSCSI (presented from a DataCore SANmelody Storage Domain Server).
However, the implementation of iSCSI connectivity in a VMware environment should only be made with the following factors in mind:
- On a VMware platform, there is additional overhead imposed by VMware in sharing the iSCSI connection over IP. Based on published information, there may be up to 3 times the overhead imposed by VMware on a shared iSCSI connection compared to a native machine without VMware. This may reduce performance below acceptable levels if multiple applications are hosted on the same physical platform without the use of a TOE card.
- A TOE card on the host platform allows the connection to be viewed and shared to the virtual machine partitions as a SCSI device. The only requirement is that there be a driver for the TOE card that is matched to the host O/S. The use of a TOE card is the recommended method for implementing iSCSI in a VMware environment.
- Today (January 2006), there are no iSCSI initiators for the ESX version of VMware. There are also no officially supported TOE cards for use with VMware's ESX host O/S.
FC and iSCSI with DataCore's Storage Virtualization
DataCore Software's storage virtualization products fully support FC in a high-availability environment, as they have for several years. Combining a FC connection architecture with DataCore's SANsymphony has been shown in independently conducted tests to deliver up to 400,000 IO's per second. This is significantly greater performance than most high-end proprietary storage arrays that cost hundred's of thousands of dollars. The comparable iSCSI performance was shown to be about 80,000 IO's/sec and was achieved without the use of TOE cards (i.e., not in a VMware environment).
DataCore Software has also published the first Storage Performance Council SPC-1 results recorded using the iSCSI standard for storage connectivity, and calls the challenging SPC-1 transaction and database-style workloads "the only objective standard for storage performance comparisons."
Compared to DataCore's Fibre Channel mark, the iSCSI results represent about half of the absolute performance (9,298.56 SPC-1 IOPS versus 19,949.73 SPC-1 IOPS for FC), but the total cost for the iSCSI configuration is also about half of the FC cost, so the price/performance of the two technologies is similar ($4.06/SPC-1 IOPS for Fibre Channel versus $4.86/SPC-1 IOPS for iSCSI) and well below the cost of proprietary solutions.
As impressive as these numbers are, and although iSCSI is suitable for many applications, it is reasonable on the basis of the forgoing discussion to expect that use of iSCSI in a VMware environment without a TOE card will accentuate the lower performance of iSCSI in comparison to FC, and raise the true cost for parity performance of iSCSI significantly above that of FC.
VMware, DataCore, and Advanced Storage Management Functions
Because the storage virtualization functions provided by DataCore run on a separate "Storage Domain Server" device, the complexities of managing a heterogeneous set of storage arrays are eliminated. In addition, the advanced functions such as snapshots and automated provisioning are independent of the VMware environment. A VM partition simply "sees" a local SCSI device, and is unaware of the storage virtualization functions and the physical storage hardware.
Summary
Use of the VMware environment for such tasks as server consolidation can be enhanced, or arguably may even require, the use of the storage virtualization capabilities that are provided by DataCore's Storage Virtualization Software products.
While iSCSI works in a VMware environment, the tradeoffs in performance and high-availability capabilities needed in an enterprise environment argue for either a FC implementation or the use of TOE cards.
Key Point Summary
Virtual Servers together with Virtual Storage enable:
- Independent scaling of storage and server resources with zero downtime
- The elimination of "best-guess" over-allocation of server compute capacity and storage capacity
- Efficient utilization of CPU and storage capacity resources, typically at 80%
- The automated provision of enterprise-wide "just-in-time" block-level storage from a single console
- Elimination of vendor lock-in. Capacity from any mix of storage arrays from any vendor can be provisioned to any application on almost any OS platform hosted by VMware®
- Rapid re-allocation of CPU and storage resources to address changing needs or disaster recovery
- Streamlining of server and storage management tasks; reduction of administration costs
- Capital cost avoidance. No fork-lift upgrades. Fewer storage and server purchases
- Simplified test and development environments
