Blog Posts

I've been a user of Fibre Channel SANs for about eight years. I have used the Dell | EMC-based arrays throughout and have gone through a few product transitions from the FC4700 to the CX-600 to most recently a CX3-80. I always liked the Navisphere management tool and was able to great performance across the range of applications that I set up to use the Fibre Channel storage.

About eight months ago I was finally convinced to try out some iSCSI arrays. First, I worked with the Dell | EMC CX3-40c, which has both iSCSI and Fibre Channel ports. This configuration didn't really seem all that different from what I was used to with Fibre Channel, mostly because I was still using Navisphere. Next, I set up and used a PowerVault MD3000i and found this array to be really easier in some ways, although it didn't have the same features in lots of respects. Finally, about four months ago I started using some Dell EqualLogic PS5000 Series iSCSI storage arrays. And I did some performance testing with them in a whitepaper that was released about a month ago. The net was that this setup is really much easier, and I was able to get great performance.

We are having a chat here on delltechcenter to discuss when to use what type of storage for virtualization, and we expect a lot of the discussion to be about iSCSI versus Fibre Channel. Feel free to join the chat or check out the transcript, depending on when you are reading this.

I haven't done a head-to-head performance comparison of Fibre Channel versus iSCSI, and I don't plan to either. I've been able to get great performance with both in the tests that I have run. It's more the ease of setup and use that makes iSCSI so compelling for me. I had resisted iSCSI for a while because I just knew that it wouldn't be good enough, but now that I have started using it I find that it works fine. I think that Fibre Channel still has places where it fits best, but I would highly recommend that iSCSI be considered for all new projects. I'm still using both in my lab. You just might find that you will like iSCSI-if you try it.

Todd

To follow up on the Hyper-V Server install video from last week, I added a new page to delltechcenter.com that shows how to configure a connection to an iSCSI storage array for Hyper-V Server. With a full Windows Server 2008 installation there is a GUI tool in Administrative Tools called iSCSI Initiator that is used to configure and manage these connections. Windows Server 2008 Core and Hyper-V Server do not have a GUI, so a command-line version called iscsicli.exe must be used.

The page that I added shows how to create a simple iSCSI connection by first enabling the iSCSI Initiator service with the sc (service console) command, then using iscsicli.exe to map the connection to the target iSCSI LUN, and then using diskpart.exe to do the partitioning and formatting. It's not as bad as it sounds, and is pretty straightforward once you know the commands.

To get an MPIO-type connection set up is only a little bit more involved. There is a script that I found in a Microsoft TechNet forum that is an example of how to do an MPIO connection to an MD3000i using iscsicli.exe. You can also use a GUI-based tool called Storage Explorer that is included with Windows Server 2008 to connect remotely to the Hyper-V server and create additional connections. (It doesn't see anything until you have used iscsicli.exe to get the initial connection.)

Todd

During last week's chat the we discussed ESXi licensing and features. In the features portion of the discussion flakrat asked if it was possible to setup two ESXi servers with shared storage to be able to do a manual fail-over of a VM between the two servers. I was able to create this setup and confirm that it works. Read on for details.

The setup that I used to test was two PowerEdge R805 servers with ESXi Update 2 refresh installed on the hard drive. This was the currently available "free" ESXi installable from VMware's web site. To install I used the Dell Remote Access Card (DRAC) virtual media capability to boot from the ESXi ISO I downloaded. I selected the local hard disk as the location to install and let it complete. Once installed, I used the ESXi configuration to set the password, IP, gateway, and hostname for each server. I then installed the Virtual Infrastructure client on a windows server and used that to manage each of the R805 servers individually.

For shared storage I used a PowerVault MD3000i iSCSI storage array. I enabled the iSCSI software initiator on each server and discovered the the MD3000i. On server A, I created a VMFS partition and created a new VM called VMTest1. I installed Windows Server 2008 64-bit Enterprise Edition. After install completed I shutdown the VM on server A. I then went to server B and rescanned the storage adapters. It found the new VMFS partition on the shared iSCSI LUN. I created a VM using the same settings as I had on Server A including the same virutal hard disk file. I then boot the VM successfully.

The most interesting part of this test was to verify that the cluster file system of VMFS was still working without Virtual Center in the picture. So with the VM still running on Server B, I tried to start it on Server A - and I got an error message that the file was in use by another server. This was great because it showed that it would not be possible to run the VM at the same time on both servers.

We will chat more about this on today's chat - ESX and ESXi.

Todd

During the weekly DellTechCenter Tech Tuesday chat a couple of weeks ago a question came up about performance monitoring with the PowerVault MD3000i iSCSI array. The initial question was how to do performance monitoring from Linux and we addressed it in a followup discussion thread. The answer at this point was to use iostat for Linux or perfmon in windows to monitor performance on each host that was attached to the MD3000i array. This lead to a follow on question which was how to monitor the performance for the entire array.

The management tool for the MD3000i, PowerVault Modular Disk Storage Manager, does not include any performance stats beyond basic iSCSI port level stats. Some investigation into the command line interface for the MD3000i revealed that there is a command to capture the performance stats on the array. Using the smcli, which is installed as part of the MDSM, it is possible to collect the performance stats for the array, controllers, and virtual disks to a csv file.

This turns out to be pretty cool and not too hard to do. Just a simple command and a little bit of spreadsheet magic and you too can produce cool performance graphs of your MD3000i. The details are posted here on delltechcenter.com.

Todd

Our upcoming chat today on benefits of iSCSI and Virtualization led me to some quick research to see what I could find. The first hit was for a Dell Whitepaper on why iSCSI is the best storage for virtualization. Turns out this is a whitepaper that I reviewed internally before it was published about a year ago.

I was a long time fibre channel user and thought that some of the points in the paper were a bit harsh. The funny thing is that reading it now I agree with it much more. The paper didn't change, but my experience in the last year with iSCSI has changed me. I really do think that iSCSI is easier and the performance concerns that I had, for the most part, don't concern me anymore. Although I must admit that I still like my CX3-80 fibre channel storage.

Todd