A comparison of AoE to FC and iSCSI protocols

One of the first issues I have to contend with when talking about Coraid storage and its use of the ATA-over-Ethernet (AoE) protocol to transfer data, is the response “Ethernet? Oh, so it’s iSCSI then?”. No it isn’t…. AoE was built from the ground up as an open source data transfer protocol, specifically concerned with finding the most efficient way to transmit raw disk I/O commands over raw Ethernet, and keeping the overhead as low as possible to maximize the throughput. In many ways AoE is more akin to Fibre Channel (FC) than it is to iSCSI in that it is a non routable protocol designed for locally based storage rather than sending data over the Internet. Like FC, AoE can be made to route over the Internet when it needs to, such as in site-to-site DR applications, but the non routable nature of the protocol makes accidental exposure of data to non authorized networks that much harder. So in order to help differentiate the data transfer protocols upon which all your networked storage systems are based, this blog entry is here to help dispel some of the myths about AoE. The only real comparison of AoE and iSCSI is that they both use Ethernet as the transport medium. iSCSI uses TCP/IP at Layer 4 and AoE Layer 2, but after that things get very different. Data delivery the iSCSI way The diagram below shows how data is sent from a client to a disk device using the iSCSI protocol.     iSCSI is a connection based topology, as is FC, and therefore requires sequenced serial delivery of the...

Making a leaner fitter Windows 7 Virtual Desktop

In our last blog post (http://blog.millennia.it/a-closer-look-at-storage-and-virtual-desktops), we touched on the IOPS issues that can mean the difference between a VDI project succeeding or failing. We have seen how VDI can produce a lot of very random I/O spikes that can cause slow or, worse for the end user, unpredictable performance throughout the working day. It is therefore important that scale testing is done as part of any VDI implementation, because what might look great with 20 VMs running could be exhibiting problems by the time you pass 100 and completely unusable before you reach 150 VMs – a problem if your wish was for 400 concurrent users! This time we look at making the best Windows 7 image so you can make sure you get the most out of your VDI implementation. This is not meant to be an exhaustive guide, but covers the main areas that can be addressed to be able to cut down the footprint of the master Win7 image, which when scaled to hundreds or thousands of user VMs can make a huge difference to resource consumption and therefore likely performance. Configure the virtual machine settings   Windows 7 compatibility – make sure that you can support running Windows 7 as a guest OS. With VMware you need a minimum of ESX 4 Update 1 on the host servers plus VMView 4.5 for official Windows 7 support. The VM should also be a version 7 VM ideally – which is easy to configure. vCPU count – Use as few vCPUs as possible while providing the required amount of CPU resource to your client VMs. Counter-intuitively...