SSDs and RAID
SSDs are becoming popular performance upgrades for notebooks and are praised for their speed and durability. However, SSDs can offer tremendous gains in performance in desktops, workstations and servers when SSDs are grouped together into RAID arrays and presented to the host operating system as a single drive. RAID storage accomplishes two main objectives:
- to make disk drives redundant so that when one fails the system will still be up and running, and without data loss, and>
- to increase the I/O performance of the storage. There are several RAID levels available that offer different levels of redundancy, performance and usable capacity. SSDs offer a new level of RAID performance never seen before with traditional hard drives.
Most SAS RAID Controllers Support SATA as Well
Most RAID controllers today that support SAS drives also support SATA drives. This means that a user can attach either SAS or SATA drives to the same backplanes and RAID controllers. Users didn’t have this flexibility several years ago with parallel SCSI and ATA technology as the two technologies had to live in separate systems. This flexibility gives the user the benefit of designating certain drives for specific workloads within the same system which has ROI benefits as well as less hardware to manage for administrators.
Until recently, most RAID controllers were designed for hard drives but since SSDs are designed to be drive-for-drive replacements, SSDs will work with most RAID controllers currently on the market today.
Kingston SSD Testing with New RAID Controllers
Kingston has tested their SSDs with several RAID controllers from third-party vendors such as Adaptec, LSI and Areca as well as RAID controllers that are built into mainstream servers. When they attached SSDs to these controllers, their immediate findings were that performance would scale as SSDs were added to the system until reaching the performance saturation point of the RAID controller. They typically found that only four to six high-performance SSDs would reach the controller’s limit.
On average, they saw read performance in the area of 1000MB/s and write performance at approximately 750MB/s on a single controller. When comparing hard drive and SSD performance we saw the largest gains in IOPS performance when testing with small 4KB files. IOPS primarily pertain to server workloads so large gains in performance can be achieved by using SSDs as a caching mechanism to cache transaction and working set files on database servers.
Benefits of Using SSD RAID
Today’s mainstream desktops and workstations feature built-in RAID controllers on the motherboard. These RAID arrays are configured in a separate RAID BIOS accessible on system bootup. Just using two SSDs in a RAID 0 stripe can double drive performance at a minimal cost. Or use two SSDs to mirror (RAID 1) your system drive in the event one drive fails the secondary drive will take over and the user is still up and running with no data loss.
In the past year or so, RAID controller designers have gone back to the drawing board to developed new RAID controller technology to address the increased performance capabilities that SSDs can offer. These changes have come in the way of new RAID processing engines, multi core CPUs and DDR3 DRAM cache buffers. Additionally some vendors are offering software with their RAID controllers to use in hybrid storage solutions where both traditional hard drives and SSDs are used together. This software identifies frequently read (“hot”) data and copies it directly into an SSD cache for superior read performance. Some RAID designers are claiming throughput as high as 2600MB/s and hundreds of thousand of IOPS from a single controller.
For servers, SSDs are ideal for small dataset applications where high-performance IO is required or for an application where a user designates a caching area on high-speed storage for transaction files, temporary database files and frequently accessed tables.
For desktops and workstations, configuring a small multi drive RAID array can offer large gains in overall system performance and accelerate applications that are IO bound by slow hard drives. RAID arrays are easy to configure and are a cost-effective way to increase performance and reliability on these platforms.
Author: Cameron Crandall – Kingston Technology