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External RAID Storage

External RAID Storage
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external raid storage

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.

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  • 0 Hide
    cruiseoveride , May 3, 2008 1:00 AM
    How does this compare to a DIY Linux Software RAID? Price? Performance? Reliability?
    Unlike a hardware solution, if the controller card dies, you can forget about getting your data back since there is no "Standard" for RAID. On Linux you could just put the drives into another PC, as the meta-data for software RAID on Linux is not going to change across different versions of Linux.
  • 0 Hide
    candide08 , May 5, 2008 7:24 PM
    Thanks for the article - you have convinced me not to even consider either of these.

    RAID 10 should be faster than any individual drive for reads and writes, and it should also be faster than RAID 5.

    Something is wrong here - either with the hardware or the tests.
  • 0 Hide
    mutsu , May 15, 2008 1:40 PM
    Actually performance isn't capped at 1 cable. There are a number of solutions that have multiple connections using iscsi, some even route between the connections dynamically on the server side and you can bond the ethernet connections on the client side to achieve performance maxing out the quantity of connections on the client machine. Of the ones that we tested (day job) there were only a few that met performance needs. All the arrays max the cable(s) out with straight read/write, but the performance on a number of array's drops drastically when you staring hitting them with more clients (20+) for read/write scenarios. Of course, these solutions are only really useful if you have, say, 100K (or more. Alot more in some cases) lying around.
  • 0 Hide
    a_k_a , August 23, 2008 6:41 PM
    It's a crying shame that storage "solution" providers (and Tom's Hardware) don't look at the needs of the laptop marketshare. This would be just what I need, but the controller cards are deal-breakers.