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RAIDing Your IDE Drives RAID is no longer just for SCSI; learn how IDE RAID can be used to soup up system performance and safeguard your data

  • May 1, 2001

RAIDing Your IDE Drives
RAID is no longer just for SCSI; learn how IDE RAID can be used to soup up system performance and safeguard your data

RAID, the Redundant Array of Inexpensive Drives, has long been a staple of network servers where speed and data security are paramount concerns. Until recently, RAID was expensive and limited to SCSI drives. Today, though, more and more PC owners are discovering that low-cost IDE-based RAID solutions can speed up systems or provide additional data security. Should you join them?

RAID Types

There are three major types of RAID arrays possible:

RAID 0 converts identical drives into an array that is the size of all drives combined. For example, two 20GB drives in a RAID 0 array would appear as a single 40GB drive. Data is transferred in a striped fashion, enabling major increases in performance compared to a single drive. RAID 0 provides no data security, however; if any drive in a RAID 0 array fails, all data is lost. This means that while performance is increased, reliability is cut in half. This will, of course, place an even greater value on making backups!

RAID 0 can also be used with different-sized drives, but in normal circumstances the additional capacity of the larger drive is wasted. For example, a RAID 0 array that uses a 20GB and a 30GB is also 40GB, unless spanning is used to capture the additional capacity. A spanned RAID 0 array using these drives would be 50GB. Unfortunately, spanning only gets you a larger drive. In fact, performance may be slightly decreased, and then of course you'll still suffer with half the reliability of a single drive.

RAID 1 uses the second drive as a mirror of the first drive; all data changes (new, changed, removed data) occurring to the first drive are immediately reflected in the contents of the second drive. This provides an ongoing redundant backup, but of course, there are no gains in performance or in storage space. In effect, you are only using half the space you have installed.

A third major RAID configuration, RAID 5, uses four drives and calculates parity information stored across all drives in the array. If any one of the drives fail, the data on the lost drive can be rebuilt. Most IDE RAID solutions support two drives in either RAID 0 or RAID 1 configurations. Some also support RAID 0+1 (aka RAID 10) which combines striping and mirroring when four drives are used. RAID 5, while expensive, makes a great deal of sense for a network server because of its combination of very high speed and maximum safety, but add-on cards supporting RAID 0, RAID 1, and RAID 0+1 are more suitable for workstations.

How Much?

Basic RAID 0/1/0+1 host adapters for two or more drives are available for around $100 from companies such as Promise Technologies (http://www.promise.com), Iwill (http://www.iwillusa.com) and AMI (http://www.ami.com). RAID 5 host adapters are available for around $350 from Promise and others. All types use a single PCI slot. If you have an older motherboard which doesn't support UDMA drives, one additional benefit is that RAID add-on boards provide support for UDMA/66 or UDMA/100 drives and all slower models.

Motherboards with IDE RAID Support

More and more motherboards from major vendors such as Iwill, Asus (http://www.ausus.com), MSI (http://www.msi.com.tw), and others now feature on-board RAID, using one of a growing number of controller chips, including AMI's MG80649, Promise's PDV20265R, and HighPoint's HPT370; the Promise and HighPoint chips are the two most widely used. Motherboards with on-board RAID have two 'extra' IDE host adapters, usually marked with contrasting plastic connectors on-board. RAID 0 and RAID 1 are supported, although you will need an add-on card for RAID 0+1 or RAID 5 implementations. While RAID-enabled motherboards are more expensive than ordinary boards, the price difference is less than the cost of an add-on board. For example, TC Computers (http://www.tccomputers.com) offers the popular Abit KT7A motherboard for around $140, and the KT7A-RAID version for around $164.

How Much Faster?

RAID 0 performance is the major reason PC users are looking at adding RAID capabilities to their systems, and RAID 0 delivers. While claims of double the performance or greater are true only under certain conditions, RAID 0 systems will almost always deliver performance improvements of at least 25% to 80% or more in a wide variety of real-world conditions. The best results are encountered when sequential data reads take place. RAID 1's drive mirroring exacts only a small performance penalty for the additional safety it provides.

Preparing for IDE RAID

If you are planning to use IDE RAID with an existing drive, make sure you have backed up your data first, since the remapping of the drive needed to set up the RAID array will delete your old data. Motherboards with IDE RAID on-board typically use an integrated BIOS-level setup program, while PCI-based RAID cards use software to set up their arrays.

Is RAID Worthwhile?

Whether you're looking for extra speed or extra safety, the answer is yes. RAID 0 provides a big speedup for disk-intensive operations, especially those which involve sequential disk reads (just make sure you keep good backups because of the loss in reliability). RAID 1 enables you to back up today's large hard drives for less than any tape backup: just buy the RAID card and an identical drive.

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