A guide to flash storage
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While all-flash arrays have gained a lot of attention in recent years, some suppliers have developed products with flash that focus on performance and value, rather than purely the fastest hardware.
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Hybrid flash arrays use a combination of flash and traditional hard disk drives to deliver improvements in performance over traditional arrays, without the need to pay all-flash prices.
Ground-up designed hybrid flash arrays differ from traditional storage arrays retrofitted with a tier of flash in existing disk slots by using flash storage in a way that targets I/O performance more effectively.
This means flash is used to accelerate all I/O, not just the data sitting on the flash tier. This approach is more effective at using the benefits of flash as there is no need to constantly restructure data to ensure that active I/O is placed on and delivered from flash, which was the case with the first flash-enabled arrays.
The benefits of the hybrid approach are obvious in terms of cost savings compared to all-flash arrays. All-flash systems can cost up to $20 per raw GB of capacity, whereas hybrid suppliers can deliver products at a quarter of that price.
For many organisations, all-flash can’t be justified because implementing a separate all-flash system simply introduces complexity into the environment. This is especially true in mid-sized organisations that don’t have multiple storage systems and are often managed and operated by IT generalists.
Many applications don’t need the low latency that all-flash solutions can provide, but do need greater I/O density (IOPS/TB) than spinning disk can deliver. Hybrid solutions can be deployed with variable amounts of flash to match performance requirements, typically starting at about 10% of capacity. Hybrid appliances are also typically more feature-rich than their all-flash counterparts, so for many organisations, hybrid solutions are a great stepping-stone towards a fully flash-enabled datacentre.
Hybrid flash systems are available from a range of startup companies, competing directly with products from the big six providers. As we will discuss, the way in which flash is implemented by these suppliers has been achieved in many innovative ways.
Nimble was founded in 2008 and was floated on the New York Stock Exchange in 2013. Its CASL or Cache Accelerated Sequential Layout uses flash purely as a read cache, placing all frequently accessed data into the cache layer either as data is written to the array or as a result of frequent read requests.
Write I/O requests are cached in NVRAM before being committed to hard disk as sequential I/O, which results in a much better use of the capabilities of spinning media and allows performance optimisation by absorbing burst and overwrite data (data written multiple times before being committed to disk).
More on flash storage
Nimble offers a range of four product categories. The CS210 and CS215 devices are aimed at small/medium organisations and scale up to an effective capacity of 106TB (with 1.2TB of flash). CS300 series arrays scale to a maximum of 606TB (effective capacity) with up to 3.2TB of flash. CS500 arrays aim at high performance requirements and also scale to 606TB, but cater for up to 6.4TB of flash (more than five times that of the CS300). For extreme performance, the CS700 offers the same capacities and performance as the CS500 with the option to cluster up to four arrays in a single scale-out system.
Tintri has focused on delivering storage to virtual environments, initially VMware vSphere but now for Hyper-V and RHEL (Red Hat Enterprise Virtualisation). The appliances also provide VDI storage for VMware Horizon View and Citrix XenDesktop.
Tintri’s latest T800 series arrays use flash and spinning disk to offer VM-centric QoS (quality of service) capabilities that are only now being made available through technologies such as VMware’s VVOLs. However, these features are provided on NFS and SMB3 file-based protocols, which will not initially be supported by VMware with the first VVOLs release.
Tintri’s current range of products scale from the entry-level T820, with 1.7TB of flash and 20TB of disk capacity, through to the T850, with 5.3TB of flash and 52TB of disk. The largest appliance is the T880, which offers 8.8TB of flash and 78TB of raw disk capacity. In each case, flash is about 10% of disk capacity.
Tegile Systems, founded in 2009, has based its storage appliances around ZFS, developed by Sun Microsystems and initially released into the Solaris operating system in 2005.
ZFS uses system DRAM and flash storage as a cache for read and write I/O to optimise the process of writing to slower hard drives, which are used as the permanent storage medium. Tegile storage optimisation and efficiency features (known as “IntelliFlash”) significantly extend ZFS and have introduced data deduplication, compression and media management capabilities.
Tegile offers a range of products that are designed for capacity or performance. The HA2100 and HA2130 platforms offer 96GB of DRAM and either 600GB or 1.2TB of flash storage, respectively. Disk capacity can scale up to 100TB or 150TB for the two models.
The HA2100EP and HA2130EP systems provide what is described as a “balanced” optimisation, favouring neither capacity nor performance. Both offer 192GB of DRAM and 1.2TB or 2.4TB of flash storage, respectively.
HA2300 and HA2400 arrays are optimised for performance with 192GB of DRAM and 1.2TB or 2.2TB of storage, respectively.
Finally, the T3400 delivers maximum performance and capacity based on 192GB of DRAM, 28.2TB of flash and up to 312TB of disk.
SDN is used as the switching mechanism to target I/O at the MicroArray serving data for a specific volume. Currently only the NFS protocol is supported.
Each DataStream 1000 MicroArray provides 48TB of disk storage, supplemented with four 1.4TB Micron PCIe SSD flash devices for a total of 54TB (raw). Currently the platform supports only RAID 1, providing a usable capacity of 26TB for each node.
X-IO has been around for some time and originated as a spinout from hard disk manufacturer Seagate.
The company sells products under the ISE brand name and focuses on selling “black-box” appliances that need zero maintenance. At the same time, knowledge of drive firmware operations allows the company to extend the life of hard drives by selectively marking only the failed part of a hard drive as inoperative, rather than taking an entire HDD out of operation. This provides a more cost-effective use of hard drives and enables zero maintenance to be achieved.
X-IO’s recently released G3 platform includes the use of flash through a new feature called Intelligent Adaptive Flash (IAF). This allows LUNs to be pinned fully into flash or to target the use of flash more effectively than simply using it as a tier within the appliance. ISE now also supports thin provisioning and QoS.
ISE 700 Series hybrid arrays start with the entry level ISE 710 G3 with 7.2TB of disk and 1.6TB of flash. This scales through the ISE 720G3 (14.4TB disk), ISE 730 G3 (21.6TB disk), ISE 740 G3 (28.8TB disk), all of which provide 1.6TB of flash. The ISE 780 G3 offers higher performance with 28.8TB of disk and 6.4TB of flash capacity.