MICRO CENTER: COMPUTERS AND ELECTRONICS
Random Access   chris, kp & rob
In The Lab
RAID & NAS
by chris

What do you use your computer for? If you are like me, it probably involves multimedia in one form or another. By multimedia, I mean digital photos, music, video as well as text and other raw data. If you have a Media Center PC, or even just a TV tuner / video capture card installed, I probably don't have to tell you how big some of these files get. Unless you are sacrificing the capture quality, chances are that the TV shows you record are just about the same size as commercial DVDs; roughly about 4 GB for each hour of video. If you tend to record many TV programs for later viewing, you probably have also noticed how small that 160 or 200 GB hard drive really is.

Expanded storage options
One solution would be to add or replace the existing hard drive with a larger one. On most systems, you will have at least one additional drive bay available to install an additional drive, but what if you have a notebook, a small form factor case, or one of the tiny flat Media Center PC cases that looks more like a stereo than a PC? Replacing a hard drive in many notebook computers, or in many small form factor computers is not necessarily difficult. But, getting your system image and software moved from the old drive to a new one can be a hassle even if you have the equipment and software to do it.

Maxtor One-Touch External Hard Drives
Maxtor One-Touch
External Hard Drives


Buffalo DriveStation
Buffalo DriveStation

A second solution is to add some sort of external storage unit such as a USB or Firewire drive. An added advantage is that these drives are portable and can be moved around and connected to other computers in the home or business. This is particularly useful for backing up or transferring very large files between systems, among other things. Drives like the Maxtor "One-Touch" series or the Buffalo Technology DriveStation include software for managing regular backups of critical data. In addition to complete USB or Firewire external drives, don't forget about external drive kits. Taking one of the external kits and installing one of your old hard drives can create an inexpensive, high-capacity storage device.

For a third solution, you could consider adding a server to your network. A basic server is nothing more than a single computer system that is sharing its storage or printer resources over the network. But, servers can also be used for much more, including managing network connections, such as a router or firewall, making web content available to the network, managing email and more. Commercial servers often differ in that they include fault-resistant or redundant hardware such as dual power supplies and RAID enabled hard drives. I'll come back to RAID in just a bit, as soon as I get done throwing around some more acronyms and jargon...

 A fourth type of external storage is what is called Network Attached Storage (NAS). Very simply, this is a set of hard drives with a minimal computer-controlled network adapter that shares its storage over a network. Some of these devices, like the Buffalo Technology TeraStation or their LinkStation, can also share devices attached to its USB ports including external USB drives and printers. The Buffalo TeraStation has the advantage of providing fault resistant storage across four hard drives in the unit. The default configuration for a unit with four 250GB drives is in a RAID 5 configuration where information and error correcting information is spread across all four drives. The available storage works out to about 750GB in this configuration. The TeraStation can also be configured to appear as four 250GB drives, a single 1000GB drive (1000 GB is 1 Terabyte, hence the name TeraStation), or as two mirrored 250GB drives.

TeraStation
Buffalo Technology TeraStation 1TB

The 1TB version of the Buffalo TeraStation can share its drives over a network using one of these configurations:

  • (4) 250GB volumes without any fault tolerance
  • A single 1TB volume without any fault tolerance
  • RAID 1 fault tolerance as two mirrored 250GB volumes
  • RAID 5 fault tolerance as a single 750GB RAID 5 volume.
I'll discuss these RAID configurations next.

Security and / or performance through RAID
RAID is an acronym for Redundant Array of Independent Disks (or Inexpensive Disks, depending on who you ask). Depending on the storage scheme, benefits of a RAID configuration compared to a single drive can include fault tolerance and error correction, increased throughput, increased capacity, or a combination of these. RAID configurations are typically identified either by the method or a numeric level. RAID features may vary from manufacturer to manufacturer, and proprietary levels or combinations of levels can and do exist.

Some of the more common implementations of RAID schemes follow:

  • RAID 0 or "striping" combines multiple drives into what appears to be a single large drive. Data is split (or striped) across both drives evenly, usually to increase performance, because disk operations can be spread across multiple drives instead of just one. No parity, error checking or data recovery is used, so if one drive in the set gets corrupted or dies, then all of the data would usually be lost. Because data is split evenly, the resulting volume will be a multiple of the smallest drive in the set. If you combine a 160GB with a 100GB drive, the resulting RAID 0 volume would have a capacity of only 200GB and not 260GB. Since there is no redundancy of data in this scheme, striping is simply an array of disks. Spanning is another term that is sometimes applied to RAID 0 since the logical volume will span all of the physical drives. The difference is that with RAID 0 striping, all usable portions of the physical volumes must be the same size, and with spanning, physical drives of different sizes can be combined into a single logical volume.
  • RAID 1 is also called "mirroring" and creates an exact copy of the data on two or more drives. Some performance gain may be seen when reading data if the specification supports accessing each drive individually, but no performance gain would be seen during write operations since data must be written to all drives in the set. The primary benefit of a mirrored drive set is that you have exact duplication of the entire drive, so even if one drive fails, the data is still available. How the manufacturer implements RAID determines if you have the ability to split and rebuild the mirror without losing or having to rebuild the entire drive set image. With the ability to split and rebuild a mirrored set, you could pull one of the drives as a snapshot backup, replace it with a blank drive and then rebuild the mirror onto the new drive.
  • RAID 5 combines striping with error checking data distributed across all of the drives in the set. Because of the addition of the error correction data, the total available storage is reduced by about 25%. (This is the default method used on Buffalo's TeraServer.) If one drive fails in the array, it can be replaced without data loss; however if a second drive fails as well, all data will probably be lost.

Some RAID controllers also support combinations of the RAID schemes, such as combining the increased capacity of RAID 0 with the fault tolerance of RAID 1. This involves creating either a striped set and then mirroring it to another striped set (sometimes called RAID 0+1), or by taking a two mirrored sets and striping them together (sometimes called RAID 10, RAID 1+0 or RAID 1&0.)

RAID Configuration Schemes

RAID0
enlarge

RAID 0 (Striped) Data is spread across all drive volumes. Drive volumes must be the same size. If one drive fails, all data is lost.

RAID1
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RAID 1 (Mirrored) Data is copied to two drives simultaneously. Mirrored drive volumes must be the same size. If one drive fails, data can still be accessed from the mirrored drive.

RAID5
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RAID 5 Data is spread across all drives, as is error-correcting parity information. If one drive fails, data can be reconstructed from the remaining drives.

Software RAID?
If you are running Windows 2000, the operating system can create and manage striped or mirrored volumes if the disk storage is first converted from Basic to Dynamic in the Disk Manager. Windows NT 4 allowed administrators to mirror volumes between drives, but did not support Dynamic Disks. DOS, Windows 3.x, 95, 98, ME and Windows XP Home and Pro versions of Windows XP have no built-in redundant storage features. (XP Pro still retains the capability to configure non-redundant volumes on Dynamic Disks as Basic, Spanned, or Striped.) This does not mean you cannot use RAID configurations with these systems, only that you must use hardware to do it.

To be able to manage your RAID set from within the OS, additional drivers and or software utilities must be installed. This can create additional steps if you are trying to install your OS to a hardware supported RAID controller; you may have to load the RAID driver during the installation process for the setup utility to detect and access the drive set. For example, when installing Windows XP, you must press F6 early in the setup process to add SCSI or RAID driver support before the target drive can be formatted and files copied. Controllers that support non-destructive conversion to RAID sets can simplify the process by allowing you to install and configure your system on a drive, and then add another drive and create a mirror at a later date. These same controllers usually will support non-destructive breaking and rebuilding of mirror volumes which can be useful in archiving the entire drive image, or quickly replacing a failing drive. If the controller does not support these features, you will have to back up all of the data from the good drive; (break the mirror, if necessary), replace the failing drive, recreate the mirror and format the set, and then restore your data to the new mirrored set.

Keep in mind that RAID schemes (other than RAID 0) are methods for increasing the reliability of the storage hardware by adding error detection and correction features to the read and write process. RAID does absolutely nothing to protect you from viruses, worms, Trojan horse programs or even accidental deletion of data. All it does is reduce your chances of data loss from a hard disk hardware failure. You still need to take precautions in day-to-day use of your computer by using a good anti-virus program, a firewall and some common sense. In addition, you should also maintain backups of any critical data or files contained on your system or network storage.

Shop Online:
Maxtor One Touch External Hard Drives
Buffalo Drivestation 250GB
Buffalo TeraStation 1TB
Buffalo LinkStations

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