As the result of ever lowering costs, IDE RAID configurations are becoming increasingly popular. However, costs alone should not be your only consideration when comparing SCSI to IDE in RAID configurations with 4 or less hard disk drives. Although SCSI is often considerably more expensive on initial implementation, it offers many advantages that will save you money in the long term. Below you will find more information regarding additional advantages of SCSI over IDE in small RAID configurations.

SCSI RAID advantages:

SCSI hard disk drives are optimized for 24 hours x 7 day operation.

The table below provides the typical mean time between failure (MTBF) values based upon anticipated operating environments for SCSI and IDE hard drives.

MTBF 1,000,000 hours 800,000 hours
Power on hours/month 732 (24 hour/day) 333 (11hour/day)
Access ratio 30% 20%
SCSI hard disk drives, in most cases, have better performance and are optimized to handle a large number of transactions in less time.
Faster data access saves time for your business.  The table below provides typical data access times for SCSI and IDE high performance hard disk drives.
Seek time 3.4 ms (15,000 rpm) 8.2 ms (7200 rpm)
Sustained data rate 30 to 58 MB/s 20 to 40 MB/s
Cache 4 MB 2 MB
SCSI offers better scalability and flexibility for RAID systems.
One of the most significant advantages to SCSI is scalability. As an example, if you needed to expand your existing RAID system to increase the amount of storage space, up to 15 additional devices (+controller) can be added to a SCSI RAID system, while IDE hard drive controllers are limited to 4.
The SCSI bus offers more features to communicate with the devices. Bus bandwidth is not the only consideration!
  • 160 MB per second bus speed for SCSI compared to 100 MB per second for IDE.
  • Command tagged queuing – SCSI controllers and hard disk drives, in order to provide the best possible bus performance, realign both commands and data.
  • Domain validation – SCSI controllers and hard disk drives exchange test sequences to insure that validity of the communication path before sending the data.  This limits data failures commonly caused by cables, enclosures, etc. System integrators eagerly take advantage of this technology.
  • Hot swapping drives and the use of spare drives can provide automatic RAID rebuild and minimize the risks when hard drive failures occur. This technology is only now becoming available to IDE controllers and drives, however it does not have the level of acceptance that SCSI hot swaps have.
  • Packetization (Ultra 320 SCSI) – Command overhead is significantly reduced with this new technology.
  • In contrast to IDE, SCSI supports a multi-controller operation.  This offers an additional level of security because it minimizes the risks of a system crash if a controller fails.
SCSI hard disk drives have a longer warranty period.
Most better SCSI hard drives have a warranty of 5 years as compared to 3 years for IDE hard disk drives.

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