ILIO Enables VDI at a 10X Performance Hike

The Atlantis Computing system saves lots of storage space.

• By Logan Harbaugh
• 01/01/2012

In most situations, the biggest bottleneck to implementing a virtual desktop infrastructure (VDI) is In-put/Output Operations Per Second, or IPOS. Many organizations find themselves buying expensive storage-area network (SAN) systems to get enough IOPS for good performance, and in fact may purchase much more capac-ity than they need to get enough disks in an array to generate the required performance. At the same time, when implementing persistent clients, total storage consumed can also be a major issue, especially at the high cost of Tier 1 storage on SAN systems.

Atlantis ILIO addresses this issue by using a large amount of RAM to serve disk requests, enabling a VMware server to handle most disk requests from memory rather than from disk, thus creating a 10-fold improvement in performance. The system also deduplicates the storage used, which means persistent clients can be created that use no more storage than non-persistent ones, saving lots of storage space while keeping users happy with the ability to configure their client as they like.

2 Modes, 1 System
The system can work in one of two modes -- as a virtual machine disk (VMDK) running on a VMware server to accelerate VDI running on that system, or as a top-of-rack system that can serve VDI storage requests for VMware, Hyper-V or Citrix storage. A typical scenario for the internal acceleration involves using four or more internal disks in the server, rather than an external SAN. Internal SAS disks or even SATA disks can provide sufficient performance in conjunction with the RAM caching, which reduces costs substantially versus a high-end SAN.

The top-of-rack model is intended to support larger numbers of clients than a single server may allow, or to support other types of VDI besides VMware. With the top-of-rack model, storage would typically be SAN-connected, or might be set up on a server with lots of internal disk storage. In either case, other than assuring that the overall IOPS and bandwidth will support the total number of clients, setup is little different than with an internal appliance.

The Atlantis ILIO system costs $120 to $150 per user for the software, plus the cost of the additional RAM (the minimum standard configuration calls for about 16GB of RAM, with the number increasing with the number of users to about 32GB for 100 users with multiple OSes). According to Atlantis Computing Inc., most of their customers see a 50 percent to 75 percent ROI because of the reduced requirement for high-performance storage, and the space savings produced by the deduplication function, along with more-responsive clients, which makes users happy.

Installation and Performance
For my testing, I first set up a vSphere 4.0 server with eight Windows 7 persistent clients, using a Synology DS509+ 10-disk network-attached storage (NAS) system connected via a dual gigabit iSCSI. I ran IOmeter from the eight clients and recorded the IOPS generated on the DS509+. I then installed the VMDK file supplied by Atlantis and configured the Atlantis ILIO software to use the DS509+.

Configuration of Atlantis ILIO is a very simple process, consisting of deploying the open virtualization format (OVF) -- installing the VMDK file to a vSphere server -- then setting the network to use, the amount of RAM to use for caching, and which disk storage to use for the volume, followed by booting the virtual machine (VM). Once booted, there are a couple of additional simple configuration steps to complete, which includes setting a static IP address and choosing how the storage is presented to the sSphere server (as NFS or iSCSI, with NFS recommended). Finally, the new volume needs to be mounted by the vSphere server, and the VMs are migrated to the new volume, or created if they don't already exist.

The store was connected to the vSphere server, and the Atlantis ILIO software was configured to use the iSCSI disk and present it as an NFS volume. The clients were migrated from the NAS storage to the Atlantis ILIO volume, which converted them to the optimized, deduplicated storage. I then ran IOmeter from the eight Win-dows 7 clients to generate lots of traffic between the server and the storage.

The number of IOPS hitting the DS509+ dropped from 3206 IOPS to 290 -- the 10-fold improvement predicted by Atlantis. In addition, boot times for each client were reduced from an average of 126 seconds to 24 seconds. The total number of IOPS reported by IOmeter on the clients went up very slightly, indicating that this number was most likely limited by network bandwidth. Given that the data being moved to and from disk was random, this represents a worst-case scenario for cache, and still indicates that around 90 percent of disk requests were being served from the RAM on the server. In a real-world environment with normal user tasks, I'd expect the numbers to be better. Further latency on the clients went down substantially, with average time for disk requests dropping from 72ms to 26ms.

Deduplication also functioned as claimed by Atlantis. With eight clients installed, the total space used on the system for the eight clients was less than one gigabyte per client after the first client was installed. That is, the first client was set up with a 40GB disk, of which 22GB was in use with the OS, Microsoft Office and other applications, along with IOMeter, a 5GB folder for disk testing. The first client used 23GB of storage on the DS509+, and the second through eighth each used about 1GB of additional space, so that eight Windows 7 cli-ents used a total of 30GB.

Once set up, Atlantis ILIO can be monitored through a Web console (see Figure 1), which provides access to reports on disk and network usage, allows you to start and stop NFS or iSCSI services, and to tune settings for caching. There's little that most users will need or want to do here, as the default settings will work fine, and other than initially setting the amount of RAM and network to use, nothing needs to be changed from the de-fault. This is very much a drop-in appliance model that shouldn't need tuning unless you increase the number of clients you're supporting.

[Click on image for larger view.]

Figure 1. The Atlantis ILIO Web console provides reporting tools for monitoring disk IO as well as network IO.

While I was unable to test with the hundreds of clients that Atlantis talks about in its case studies, extrapolating from the results I obtained confirms that the system should work as well at higher numbers of clients, and At-lantis has case studies of implementation of thousands of VDI clients to back up the company's claims.

Providing users with an experience as good as -- or better than -- they'd get with local PCs is critical to the long-term success of a VDI project. Atlantis ILIO provides a means to remove the storage bottleneck from the equation when creating a large VDI implementation, which should substantially reduce the cost to duplicate or improve on local desktop performance with a VDI system. In fact, by providing boot times substantially faster than even fast desktop systems, Atlantis ILIO could make a VDI system more attractive to users than having their own PCs.