Level—Intermediate

RAID (Redundant Array of Independent Disks) are a simple, cost-effective solution that can help you improve your system's overall performance. This TECH TIP will help you set up your system to run the OS (operating system), applications, and virtual memory on a RAID drive.

A RAID disk drive employs two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally used on personal computers.

The advantage of using a RAID disk drive  with your CAD workstation is the ability to speed access to the disk, application, and OS. A RAID employs multiple drives to break up the tasks across multiple disk drives. The user only sees one drive, but the OS can access multiple disks at the same time.

Types of RAID disk drives

• Level 0—Striped Disk Array without Fault Tolerance: Provides data striping—spreading blocks of each file across multiple disk drives—but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.

• Level 1—Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.

• Level 2—Error-Correcting Coding: Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level.

• Level 3—Bit-Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used.

• Level 4—Dedicated Parity Drive: A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks.

• Level 5—Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.

• Level 6—Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks.

Most workstations come with an SCSI controller which can be configured to use multiple drives in a RAID disk drive set.

Configuring your System

The first decision is the level of RAID to use. For most CAD users, RAID level 0 is the simplest and least expensive solution for speeding disk access. RAID level 0 will require 2 disk drives. This will put some of the information on one disk and some on the other (stripe) and access both disks to speed access.

The downside of this level is that if either drive fails, there is no redundancy. This means any data or applications on the computer would be lost if either drive fails. This is slightly more risky than the one-disk setup most systems use.

There is no need to go to the expense of setting up a RAID level 5, hot swappable drive set for a workstation. This is typically used on servers that need high availability and cannot be down.

Virtual memory

Another option in addition to setting up the RAID drive for the OS and applications is to have another disk drive for virtual memory. This is the space used by the OS kernel. Putting this item on another disk drive, and disk controller if available, can also improve speed for your system.

Conclusion

Setting up your system to run on a RAID disk drive can make a significant difference in system performance. Use another disk drive for the virtual memory to further increase your performance.

One good way to justify this in your environment is to set up some performance tests and run it against two systems, one with a RAID drive and one without. Also test the virtual memory on another disk drive.