SCSI Performance for an ATA Price

By Logan Harbaugh (Send Email)
Posted Nov 22, 2002

Escalade 7500-4 ATA RAID Controller: A high performance disk controller that uses ATA drives rather than the much more expensive SCSI drives 3Ware's ATA RAID controller is, in most cases, an excellent solution for enterprises looking to save on hardware expenditures. The high performance disk controller uses ATA drives to deliver hard drive performance equal to or better than SCSI, for half the price.

For all but the largest database servers, 3Ware's Escalade technology delivers hard drive performance equal to or better than SCSI, at half the price. It allows RAID 0, 1, or 5 configurations with two to 12 ATA 100 or ATA 133 drives, and it delivers great performance with the less expensive drives.

At the workgroup level, the biggest difference between a regular PC and a server is that the server generally has SCSI drives and a SCSI controller instead of a standard ATA controller. This is because SCSI is assumed to have higher performance than ATA. A long time ago this was true, but the performance differences between drives these days are relatively small. The differences between controllers aren't all that large any more either, especially with the new, high-end ATA RAID controllers.

With a reasonable number of drives attached to a controller, the limiting factor becomes the controller's ability to handle bandwidth, or even the PCI bus' ability to handle bandwidth, with either ATA or SCSI.

The Escalade 7500-4 ATA RAID Controller

Source: 3Ware

We tested 3Ware's four-drive ATA RAID controller to see how much performance can be achieved with ATA. The test environment was a Gateway 7300 Pentium II Xeon/450 dual-processor server with 512 MB of RAM. The server was already equipped with Gateway's ADAC Ultra2 RAID controller and four Seagate SCSI drives.

The Cheetah ST39102LC Ultra 2 SCSI SCA drive has a capacity of 9.1 GB and spins at 10K RPM. Ultra2 SCSI is rated at 80 Mbyte/sec maximum. We added the 3Ware Escalade 7500-4 four-port ATA RAID controller, with four Maxtor DiamondMax 80 UltraDMA 100 81 GB drives, spinning at 5400 RPM. ATA 100 is rated at 100 Mbyte/sec.

Both arrays were set up as RAID 0, i.e., one volume spanning all four disks. The bottom line: The Escalade controller and the ATA drives had a much higher throughput than the Ultra2 SCSI drives and controller, and at a cost-per-gigabyte less than one-third that of the SCSI drives.

SCSI vs. 3Ware Performance Comparisons
Total Formatted Capacity 33.8 GB 305 GB
Sequential Reads 34.7 Mbytes/sec 61.5 Mbytes/sec
Sequential Writes 32.1 Mbytes/sec 47.3 Mbytes/sec
I/Os/sec 353 268

The astute reader will note that Ultra2 SCSI is relatively old, and that the new Ultra160 and Ultra320 SCSI interfaces are capable of much higher throughput. This is true, theoretically. In fact, the maximum throughput from a system is usually limited by the number of drives. One drive will not sustain a 320 Mbytes/sec, or even 160. Further, a 32-bit PCI bus will not sustain 320 Mbytes/sec -- 160 Mbytes is about all you can get without moving to a 64-bit, 66 MHz bus speed.

SCSI does have one other advantage, however: hot swap capability. Hot swap capability requires either Serial ATA drives or special hardware to be accomplished with the 3Ware card. An ATA hot-swap drive cage is also available from 3Ware.

The number of I/Os per second is higher with the SCSI raid array. This is because the RAID controller uses an Intel i960 processor and 16 MB of RAM. While the number of I/Os per second was at one time a crucial differentiator for database performance, this is not usually the case any more -- most databases queue up multiple small requests into one larger request. For most other server applications, such as file, print, application, and Web services, throughput is a more effective indicator of performance, and the 3Ware card certainly performs.

The cost factor is dramatically different. Duplicating the Ultra2 SCSI drive array used for testing would cost about $250, using the lowest prices available on www.pricewatch.com. This assumes an inexpensive Ultra2 SCSI RAID controller and the same drives, and results in $6.94 per GB. The 3Ware controller has a list price of $369, but pricewatch shows it at $252. With the same Maxtor drives, this configuration would total $632, for nearly 10 times the capacity -- 305 GB formatted vs. 32 GB formatted for the SCSI system, and $1.97/GB. A new Adaptec Ultra160 RAID controller and four IBM 73 Gb Ultra160 SCSI drives would cost $252 for the controller and $295 each for the drives, totaling $1,432, or $4.90/GB, for 20 GB less storage than with the 3Ware controller.

For those looking for even higher performance, 3Ware offers a Serial ATA version of its card. Serial ATA drives offer hot swap capability, and the drives are capable of higher performance as well. According to 3Ware, tests with eight-drive systems have resulted in sustained throughputs of 160 Mbytes/second for reads, and 70 Mbytes/second for writes in a RAID 5 configuration.

Vendor Home Page: 3Ware
Sever Home Page: 3Ware Escalade 7500-4 ATA RAID Controller
Price of Server Setup as Tested: List price is $369, but the product is available from various resellers for less
Other Noteworthy Features: Drivers are available for all versions of Windows, Red Hat Linux, and SuSE Linux

Pros: Very high performance, even relative to SCSI, for a much lower price; Supports ATA 100 and 133 drives, which are climbing in capacity faster than SCSI drives; A serial ATA version offering even better performance is also available from the vendor
Cons: No NetWare support; ATA doesn't support external drive enclosures; Expansion is limited to a maximum of 12 drives

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