I can’t state it enough. When you are designing a virtual desktop environment, you need to correctly size the back end storage correctly. I have been involved with several VDI deployments, VMware View in particular, and storage performance can make or break a successful deployment. If you don’t believe me, take a look at one of my other posts here. That being said, how are you supposed to scale your virtual desktop POC from 100 users to 1000 knowing that the impact to your storage I/O load will be going through the roof? The quick and unqualified answer is Solid State Drives. With ratings over 4000 IOPS per disk, they easily outpace 15k SAS drives rated for 180 IOPS and can take the 100-fold hit to your I/O without blinking. The down side is most storage vendors are still only supporting 100 GB SSD drives, so capacity is a problem. How does EqualLogic overcome the performance/capacity issue with SSD drives? It’s Magic… It’s Bleeping Magic.
Last summer, EqualLogic released their Hybrid PS6000XVS. This array combined eight 100GB SSD drives and eight 600GB 15k SAS drives within a single 16 drive enclosure. A proprietary RAID type allowed each volume to be stretched across both sides of the array, both SSD and SAS. The two sides of the array have different I/O and performance profiles, and the EqualLogic controllers are aware of the differences in capacity and performance. When data is written to the Hybrid array, incoming data pages are tagged as ‘hot’ by the system. This is a rating of relative activity of pages within the array. Recent reads and writes to the data marks the page as ‘hot’. As read/write activity tails off, the page becomes ‘cool’ and even ‘cold’ if the page hasn’t been accessed recently. Write activity automatically mark a page as ‘hot’.
Since the EqualLogic controllers know that the SSD drives have a higher performance profile than the 15k SAS drives, the data is written to the highest performing area within the array, which is the SSD drive set. Continued reads will keep the data page ‘hot’, but inactivity for a specific page will cause it to ‘cool’ off relative to other pages. Once a threshold is reached within the array, the data page is then moved (on the fly) over to the 15k SAS side of the array but still within the same volume.
This process continues to occur as new data is written to the volume, leveraging the high performance of the SSD drives and the higher capacity of the 15k SAS drives to optimize data page placement within the volume. If a data page that resides within the 15k SAS side of the volume is accessed for reads or writes, the temperature of that data page increases. Once the temperature of a page on the 15k SAS drives rises above a page that resides on the SSD side, the two pages are swapped (on the fly), therefore optimizing data page placement within the volume.
As you can see above, the ‘colder’ pages move to the lower tier of storage, while the ‘hotter’ pages are migrated to the highest performing level. This optimizes data placement within the array and grants SSD level performance for all of the data within the volume while extending capacity with 600 GB SAS drives.
When considering VDI rollouts and the increased performance demands that a View infrastructure requires, it is easy to see that the PS6000XVS Hybrid array is a welcome addition to the storage toolkit. By leveraging a Hybrid array, we can easily provide +30 thousand IOPS within a single enclosure with a couple TB of capacity. This is a game changer in the VDI world, and one you should consider, especially if you are using EqualLogic storage. If you are deploying VDI without considering one of these Hybrid arrays, Caveat Emptor.