External RAID Storage

Direct Attached Storage is not Dead Yet

There are many ways of attaching storage solutions to a PC system. While direct attached storage based on internal controllers and hard drives dominated the PC world in the 1990s, flexible external storage solutions are gradually taking over. Thanks to a broad selection of interfaces such as eSATA, SAS, Fibre Channel and Ethernet, storage solutions have moved out of the PC, and can increasingly be found in the form of powerful NAS solutions, DAS boxes and SAN appliances. However, flexible networked storage solutions are still rather expensive, and can mostly be found only for rack installation. Also, few of them provide the throughput or I/O performance required by performance critical applications. We looked at two direct attached, entry-level RAID storage systems that aim to bridge the gap between inflexible high-speed internal storage and flexible, but expensive networked storage solutions.

While networked storage solutions based on Network Attached Storage (NAS) or Storage Area Networks (SAN) over Ethernet clearly are our favorite choice for near-line and offline storage, they often cannot satisfy the demands of online and high-performance storage applications. Offline storage describes backup storage, archiving or secondary storage areas, which do not need to deliver high performance. Near-line storage is characterized by frequent access — such as daily backup or fileservers — although near-line storage doesn’t have to provide maximum performance either. That is needed most by online storage, which refers to high-performance RAID arrays and storage solutions to power databases, your operating system or temporary files such as huge video streams.

Like SCSI hardware did a few years ago, SAS controllers and storage appliances fulfill all the requirements of online storage today. However, SAS hardware comes with the price premium of professional products. SAS controllers using SATA hard drives are sometimes an option, but you still have to invest in a powerful storage controller and appropriate storage appliances. NAS devices and SAN/iSCSI storage are positioned on the other end. There are certainly affordable solutions, but these don’t really satisfy higher performance requirements. Both NAS and iSCSI are limited by the network performance (roughly 110 MB/s for Gigabyte Ethernet); interface options such as Fibre Channel are too expensive.

This is where Accusys’s iRAIDer and AMCC’s 3Ware Sidecar make their appearance. Both consist of a PCI Express RAID controller card, which you’ll have to install into your host PC, and an external storage box for up to four SATA hard drives.