Solid state-only systems come in two forms right now. The first and most common are systems that are designed primarily to address a specific performance problem in the environment, but have limited storage services capabilities like snapshots or replication. These can be used to boost performance of a poor performing database, a poor performing VDI boot, or even a storage area for extremely popular files on a NAS or Cloud Storage system. In these cases, the data set in its entirety is moved to solid-state disk (SSD) and that data area is not swapped out continuously as a caching system would. Essentially the data is "pinned" to SSS. While this inhibits the broad application of solid state, it does lower the turnover rate of the data in the SSS. The less turnover of data should mean less potential writes, which are the great enemy of flash-based systems.
Consider this type of SSS a more surgical strike against performance and with that comes better cost control and possibly better product selection. Cost is reduced because only the capacity needed to accelerate the specific data set needs to be purchased, which could be a fraction of the size of a cache. If in the rest of the environment the extra performance boost that SSS will provide is more of a "nice to have" rather than a "got to have," then just isolating to a dedicated SSS may be a better option for you.
A dedicated SSS also gives you the ability to be more granular in your product selection. This can come in terms of how the SSS is attached and what type of SSS you use. If it is a single server that has the data set to be accelerated, then a PCIe SSD may be appropriate if the data set is shared, which is common in highly available configurations. If multiple servers have data sets to be accelerated then, a Fibre Channel-, Ethernet-, or Infiniband-attached SSS may be a better choice. Also, as we discuss in our article "The Advantages of DRAM SSD" that approach also provides the flexibility to select DRAM-based SSS, which is ideal for high write I/O environments.
The other option in solid state-only systems are those that the entire primary storage tier is solid state-based. Basically it is a traditional storage system, but with no mechanical drives. As a result, no tiering needs to take place. These systems, as we described in our article "Innovative Flash Demands Data Services," offer the complete range of storage services that you have come to expect from a primary storage system like snapshots, replication, as well as multiple protocol support like CIFS, NFS, and iSCSI. The other value of these systems is that since ALL data is now on flash, there is not copying back and forth between tiers as there is with caching or automated tiering technologies.
The challenge, of course, for flash-only primary storage is keeping the price in an affordable range. These systems are going to have to leverage either compression, deduplication, or both to maximize the capacity of the premium-cost flash memory. The trade off may be a loss in performance and, while that may be an issue compared to a dedicated SSS, your environment may just need something faster than 15K RPM-based arrays, not something as fast as a pure SSS appliance. As a result, the SSS intended for primary storage may be a very cost effective alternative.
As always, the answer in choosing a memory only-based storage system or a system that has a mix of SSS and mechanical drives is largely dependent on your environment. If you have a broad workload that can benefit from the flash-based performance boost, then tiering or caching may be in order. If you have a very specific or write-heavy workload, then a dedicated SSS may be the better approach. Finally, if you are ready for a storage refresh and you are looking to improve performance and reduce power consumption, then a flash-only primary storage tier may be the best fit.
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