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Due to the lower cost, IDE RAID configurations are becoming more and more popular. However, cost should not be the only consideration when comparing SCSI to IDE in RAID configurations with 4 or less hard disk drives. SCSI offers a lot of advantages which save money in the long term. The following information describes the additional advantages of SCSI has over IDE in small RAID configurations.
SCSI RAID advantages:
SCSI hard disk drives are optimized for 24 hours x 7 day operation.
SCSI hard disk drives have better performance and are optimized to handle a large number of transactions in less time.
SCSI offers much better scalability and flexibility for RAID systems.
The SCSI bus offers more features to talk with the devices. The pure bus bandwidth is not the only difference.
SCSI hard disk drives have a longer warranty period.
SCSI hard disk drives are optimized for 24 hours x 7 day operation.
The following table shows the typical mean time between failures (MTBF) values and operating environments for SCSI and IDE hard disk drives.
SCSI MTBF 1,000,000 hours Power on hours/month 732 (24 hour/day) Access ratio 30%
IDE 800,000 hours 333 (11hour/day) 20%
SCSI hard disk drives 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 following table shows typical data access times for SCSI and IDE high performance hard disk drives.
SCSI Seek time 3.4 ms (15,000 rpm) Sustained data rate 30 to 58 MB/s Cache 4 MB
IDE 8.2 ms (7200 rpm) 20 to 40 MB/s 2 MB
SCSI offers much better scalability and flexibility for RAID systems.
If you need to expand your existing RAID system to increase the amount of storage space, additional SCSI hard disk drives can be added to SCSI RAID systems. Normal SCSI controllers can handle up to 15 devices (+controller). The number of IDE hard disk drives is limited to 4.
The SCSI bus offers more features to talk with the devices. The pure bus bandwidth is not the only difference.
160 MB/s bus speed for SCSI compared to 100 MB/s for IDE.
Command tagged queing - SCSI hard disk drives re-order commands and data to offer the best performance on the bus.
Domain validation - Test sequences are exchanged between the SCSI controller and the hard disk drive to test the communication path before sending the data. Failures, which are caused by cables, enclosures, etc. are limited. System integrators can take advantage of this technology.
Hot swapping and the use of spare drives can provide automatic RAID rebuild and minimize the risks when hard disk drive failures occur.
Packetization (Ultra 320 SCSI) - Command overhead is significantly reduced.
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.
SCSI hard disk drives normally have a warranty of 5 years compared to 3 years for IDE hard disk drives.
Die neuesten SCSI-Platten haben mittlerweile eine MTBF von 1.200.000. Damit dürfte die Frage nun endgültig beantwortet sein.
Kein Dauerbetrieb mit IDE!
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