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What is a storage accelerator and what are its advantages? Why not use a solid-state drive?
An I/O accelerator, or storage accelerator, is a complete, high-performance solid-state storage subsystem implemented on a PCI Express (PCIe) card.
Fast solid-state memory used as the storage medium eliminates the mechanical latency and slow read/write performance of traditional mechanical storage devices. The memory is accessed through the server's PCIe slot for much faster data transfers than from those using common serial disk interfaces, such as serial-attached SCSI (SAS) or Serial Advanced Technology Attachment (SATA). However, an I/O accelerator is designed to mimic the block storage behavior of a standard disk.
As multiple high-performance workloads compete for the server's finite computing resources, system bottlenecks can quickly pile up. Perhaps the most vexing computing bottleneck centers on the local storage subsystem when moving virtual machine files and application workloads between fast processing and far slower disk systems across an aging SAS/SATA disk interface.
The principal benefit of an I/O accelerator is the improvement in storage access time and IOPS. In a server-agnostic I/O accelerator such as the ioDrive2 from Fusion-io, for example, the unit comes in storage capacities of 365 GB, 785 GB, 1.2 terabytes and 3.0 TB. However, the largest storage accelerators can provide read-access times of 69 microseconds and write-access times of 15 microseconds, with 136,000 random-read IOPS and 242,000 random-write IOPS.
By comparison, a 15,000 rpm SAS drive provides between 175 and 210 IOPS across a standard SAS disk interface depending on the disk itself, the load of other disks on the interface and several other factors. Still, an I/O accelerator can provide about 1,000 times more storage IOPS than a conventional disk setup.
Although storage accelerators will work for any physical or virtualized workload, the cost-benefit is greatest for applications that require heavy storage access, such as databases and all types of data analytics -- including big data tasks.
There is some confusion between I/O accelerators and solid-state drive (SSD) devices. Both rely on solid-state memory as the storage medium, but the interface is very different. Since SSD units are designed to coexist with mechanical disks and exchange data across a conventional SAS/SATA interface, SSDs also inherit the inefficiency of those interfaces. I/O accelerators forego the standard SAS/SATA disk interface in favor of fast PCIe data transfers. PCIe is more capable of keeping pace with the storage accelerator's onboard memory.