SecurityDude, CISSP-ISSAP is an IT consultant, Security & Privacy Advocate and blogger at large with over 20 years IT experience. SecurityDude shares tips, tricks, and info that the average networking professional will find interesting and indispensable.
It is very likely that in the last 10 years, virtualization has made an impact on the way you design and operate your IT infrastructure. The VMWare company (now part of EMC) in particular has created a very successful business by allowing us to install multiple virtual hosts on a single physical machine. The fact is, most of our servers are woefully underutilised and virtualization is a great way to get a better ROI.
It also lowers the requirements for power and HVAC by reducing the number of machines needed. If you are involved with Data Center operations, you are painfully aware that power and cooling are even more expensive than the equipment.
This story isn’t about VMWare per se, but using virtualization to solve a pesky storage problem. In my previous posting Inexpensive Enterprise Storage, I introduced readers to storage networking company Coraid. Since writing that article, I have maxed-out my SR1521 storage shelf by adding another 5 500Gb hard drives. There are now 15 500Gb drives for an aggregate capacity of 7.5Tb. I originally planned on waiting for the cost of 1Tb drives to drop further, but I found a smoking good deal on 500Gb Seagate Barracuda ST3500320AS drives via Pricewatch. Antares Digital (who I found on Pricewatch) has the drives for $67.00 each with free shipping.
The problem I faced once I powered the monster up was “how will I divide the space?”. I am pretty conservative when it comes to storage, so I opted to create three RAID 5 goups of 5 drives each. This does not leave me with a hot spare, but the RAID group size is small enaough that I don’t worry (too much) about a multi-drive failure scenario. When RAID 6 becomes available, I may opt for one large RAID 6 group and a hot spare or two. The result of the current configuration is 3 LUNs at 2Tb each. I lose 1.5Tb capacity to the RAID 5 parity drives, but I consider that cheap insurance.
Once I arrived at this configuration and waited for the RAID groups to finish building, I realized I STILL had a poroblem. The three LUNs can only be allocated to three hosts. I have nine hosts I need to share the storage among. I discovered that what I needed was an LVM (Logical Volume Manager). An LVM does for storage what VMWare does for hosts. An LVM allows you to take all of the LUNs in one of more shelves of drives and turn them into a large pool from which any number of virtual LUNs can be provisioned. One of the really cool benefits of the way storage virtualization works is that you can dynamically shrink or grow existing virtual LUNs at any time.
My first thought was to save money by using one of my Fedora box to run LVM2 to virtualize my storage pool. Yikes! LVM2 isn’t the easiest thing to understand and configure unless you have a LOT more Linux admin experience than me. Then, there is the problem that the Fedora server could crash and take all of the LUN mapping metadata with it and render my data unreadable. I suppose I could have built a Linux cluster, but again, I really lack the necessary expertise. Instead, I got out the ‘ol checkbook and bought another Coraid product. Their VS21 stoage virtualization applicance does what LVM2 does, but it is very simple to setup. I had the VS21 configured and serving requests in under an hour. It sits between hosts and your storage shelves and acts like a proxy agent. The VS21 responds to host request for LUN access and translates the block requests to where it has them mapped in the pool of disks. It was another $2995.00, but I consider it a solid investment for the provisioning flexibility it affords. It is a flash-based system with dual power supplies and no internal hard drive. Because there are no moving parts (other than fans), I expect reliability to be superior.
Tags: storage, vmware, virtualized storage, storage virtualization, EMC
