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STORAGE SWITZERLAND

RESOLVING THE $ PER GB PROBLEM OF SSD IN VIRTUAL ENVIRONMENTS

George Crump, Senior Analyst

The problems caused by a virtual desktop or within The All Flash Resolution a storage infrastructure have been well documented. There are performance issues caused by the extremely There tends to be two approaches to resolving the random I/O (Input/Output) of dozens of virtual machines demands placed on storage systems by on each host. There is also a storage capacity concern as projects and to do so affordably. The first is to use a flash server and desktop storage that used to be direct only storage system. This certainly will resolve most of the attached to each physical server is now moved to a performance issue. Flash is well suited to the random shared storage device. Striking the right cost/performance workloads of the virtual environment. balance is critical so that the virtual project can continue to deliver and improve on its ROI (Return On Investment). To address the cost issue, these systems will often use inline deduplication and compression to reduce the In large part the solution to the performance challenge is effective cost of flash storage by being able to store more the intelligent use of solid drives (SSD) within storage on that tier. The trade off is generally worthwhile in all systems. Most virtual environments can generate more flash systems. While there are extra steps required to than enough I/O demand from the storage system to verify redundant data, the speed at which flash can justify the use of SSDs. However, unlike systems those steps and the value of increasing by as they can’t always generate “profit per IOP” (Input/Output much as 5X the effectiveness of a premium platform is a Operations Per Second) that is needed to justify the cost worthwhile trade-off. of an SSD. This means that, especially in the mid-rage data center, a balanced approach between SSD and HDD The challenge is that an all-flash system, even with (Hard Disk Drive) is needed. optimization, is still going to be too expensive to slide in under budget. This leaves data centers looking for other options. Finally these systems tend to be only, which leaves the data center looking for a alternate storage system for their file services.

[1] The Hybrid Resolution system but these systems bring the deduplication and compression that flash systems leverage, to a mixed array. Another option is to use a hybrid SSD model where a small The impact is a significant reduction in the cost per GB of amount of SSD is used in the storage system to the the virtual storage infrastructure, while making the flash most active data but with little to no optimization to area more productive. Like standard hybrid arrays these improve storage efficiency. These systems also attempt to systems also provide SAN and NAS services but now they reduce costs by providing NAS and SAN capabilities in a have the capacity optimization to allow a single system to single package, reducing the number of storage systems potentially meet the entire data center’s performance and that the storage manager needs to manage. capacity needs.

Hybrid systems gain their cost efficiency by using hard disk The key is to provide this functionality without impacting drives for less active data and SSD for active data. They performance. also resolve the performance problem, as long as the needed data is in cache, but the risk of a cache miss or data being delivered from the HDD is obviously higher than HDD Deduplication without Performance Impact a flash only system. Deduplication requires a significant amount of meta-data This means that the HDD storage area has to perform management and lookups. If this work has to be done on adequately to provide adequate performance to the an HDD, the of the hard drives as they rotate into 15-20% of data that will initially be read from hard disk due position will likely create a noticeable performance impact. to cache misses. To compensate, these systems tend to Flash systems avoid this problem because they don’t have sacrifice deduplication and/or compression in order to hard disks to deal with and meta-data is stored on flash make sure that hard disk performance is not impacted just like the actual data. significantly. Eliminating the overhead of deduplication maintains the performance of the hard disk area but Meta-data information does not need to be stored on the decreases its cost effectiveness. Also, the SSD cache is same storage area as the actual user data though. There often not optimized either which means that it may not be are many examples in the storage industry of companies used as efficiently as possible. storing other types of meta-data on faster mediums like SSD. Hybrid optimized storage systems leverage the ability The result is that even though they can perform multiple to store meta-data separately from the actual data and functions (SAN and NAS), eventually more than one hybrid store the deduplication information on flash. system may be needed because capacity limits of the HDD or SSD storage are reached. As with any other environment The value in making this split is that deduplication can now more systems means added management and additional be applied universally on both hard disk and solid state cost. disk. Making a cost premium storage area like SSD, 5X more capacity efficient, reduces the amount of flash storage needed and the overall system cost as a result. The Hybrid Optimized Resolution Even though hard drive pricing is already very affordable, there is still a hard cost associated with acquiring, Hybrid optimized storage systems like those from Tegile powering and cooling them. The less hard drives needed Systems take a best of both worlds approach. This type of the better. system has similar functionality to a standard hybrid

[2] Leveraging DRAM to Improve Performance Hybrid Solutions like Tegile’s that are connected via a high speed storage network and have the ability to pin certain To process this meta-data, inline hybrid optimized storage data volumes in the storage systems’ flash memory can systems like Tegile’s can also leverage DRAM (Dynamic provide this capability without the extra expense and Memory). Similar to flash, DRAM has more management of a separate card in each host. This allows than one purpose in the system. First, DRAM is used to for the density of the virtual machines on the host to manage data ingestion so that it can be quickly analyzed increase dramatically since the limitation of DRAM is for redundancy. Again, the comparison is DRAM storage removed. It also allows the density to be achieved while communicating with flash storage for rapid results. The keeping costs down, since high performance virtual DRAM is also used to cache the most active read data. memory almost comes along free. Writes are also cached but to flash for an extra layer of protection in case of power failure. Summary

Leveraging Hybrid Storage To Optimize Host Memory Hybrid optimized storage systems can help resolve both the $/GB that many virtual environments are facing as well Another benefit of flash is that it makes an ideal location for as the overall shortage in IOPS. The ability to limit and storing for RAM paging and swapping when control capacity growth through deduplication and DRAM resources are maxed out on the host. Flash compression should also lower the number of systems responds almost as fast as DRAM so the virtual machines required. Many mid-sized data centers may only need one, will notice almost no performance impact as a result of the which of course further reduces cost and complexity. virtual to real memory swap. Many vendors will suggest that this be done on a separate flash card inside the server. Which of course adds to the expense.

About Storage Switzerland Storage Switzerland is an analyst firm focused on the virtualization and storage marketplaces. For more information please visit our web site: http://www.storage-switzerland.com Copyright © 2012 Storage Switzerland, Inc. - All rights reserved

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