RAID 0: Hype or blessing?

We continue our stopwatch measurements with a file transfer performancetest. The dataset contains snapshots with a total size of 535MB and an average file size of 4.5MB. In RAID 0 and single drive configurations the files were copied from and to the same partition. In the configuration with the two independent disks, the files of the first disk were cloned to the second disk. This is, of course, a best case scenario for the independent configuration. In daily practice it's not always possible to plan a filetransfer in such a way that both disks can be put to work simultaneously.

In spite of the optimum scenario for the configuration with two independent disks, the RAID 5-configuration crossed the finishline first. The exceptional performance of this controller in this case - the MegaRAID SCSI 320-2X is nearly three times faster than the next RAID configuration in line - can be attributed entirely to its enormous cache. In second place we find the Raptor WD740GD disks, trailed at respectable distances by the Raptor WD740GD and WD360GD stripe configurations. RAID 0 shows its usefulness in file duplication: the Raptors in RAID 0 are approximately 32 percent faster than their solitary operating brothers .

	File copy (seconds)
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		10,2
	Raptor WD740GD		2		Dual		FastTrak S150 TX2plus		16,8
	Raptor WD740GD		2		RAID 0		FastTrak S150 TX2plus		28,2
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		28,7
	Raptor WD740GD		1		Single		FastTrak S150 TX2plus		41,3
	Raptor WD360GD		1		Single		FastTrak S150 TX2plus		42,1

Launching the Kaspersky virusscanner results in a light increase in transfer times for single drive and RAID 0-configurations. The MegaRAID SCSI 320-2X and the independent Raptors are more hindered by the virusscanner's presence; obviously, the MegaRAID uses its cache less effectively. Nonetheless, in an almost Schumacherian way the MegaRAID manages to win this race as well.

	File copy + Kaspersky virusscan (seconds)
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		22,0
	Raptor WD740GD		2		Dual		FastTrak S150 TX2plus		26,8
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		32,0
	Raptor WD740GD		2		RAID 0		FastTrak S150 TX2plus		32,8
	Raptor WD740GD		1		Single		FastTrak S150 TX2plus		43,2
	Raptor WD360GD		1		Single		FastTrak S150 TX2plus		43,9

The test continues with measuring how long it takes the configurations to boot Windows and start-up Photoshop CS. Photoshop produced a few unexpected results on a number of configurations, since in some cases startup times were seconds lower than during previous testruns. Scratch file creation was probably the cause of these erroneous differences, and therefore they have not been included in the comparison table. Striping or subdividing hard disks doesn't seem to deliver spectacular performance improvements. Nevertheless, there were still some noticeable differences to be found.

	Photoshop CS start-up time (seconds)
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		7,8
	Raptor WD740GD		2		RAID 0		FastTrak S150 TX2plus		8,6
	Raptor WD740GD		2		Dual		FastTrak S150 TX2plus		9,6
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		9,7
	Raptor WD740GD		1		Single		FastTrak S150 TX2plus		9,8

The Windows boot time was measured between the moment the POST-screen disappeared and the LOG IN screen appeared on the monitor. The RAID 0 arrays perform significantly better than the single drive configurations, resulting in 31 to 37 percent lower boot times. Similar to starting up Photoshop, the two independent Raptors are hardly faster than a single disk. Disappointing is the time of the MegaRAID SCSI 320-2X. In the first seven seconds of starting up Windows the MegaRAID showed no disk activity, which resulted in higher boot times. Starting up fast is a lost race for the MegaRAID because initializing the controller and the SCSI-channels takes too much time.

	Windows XP boot-up (seconds)
	Raptor WD740GD		2		RAID 0		FastTrak S150 TX2plus		8,4
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		9,2
	Raptor WD740GD		2		Dual		FastTrak S150 TX2plus		11,7
	Raptor WD740GD		1		Single		FastTrak S150 TX2plus		12,2
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		13,1
	Raptor WD360GD		1		Single		FastTrak S150 TX2plus		14,6

The results shown earlier are perhaps disappointing for those who follow the teachings of Storage Review and share a rock-solid belief in the uselessness of RAID 0 on the desktop, but we've got good news for them: RAID 0 can be a slower configuration! The two tests mentioned below are examples of this. The first test was installing Windows XP Service Pack 1. The light overhead of striping during the handling of small requests in a situation with minimum I/O queue, is probably the reason why RAID 0 is slower in this case. Although you would not expect it directly, the processor load is considerably high during the installation of SP1 updates. The MegaRAID 320-2X SCSI's higher performance is due to the large write-back cache (which makes faster I/O writes possible), in addition to the lower access times of the Atlas 15K disks.

	Windows XP SP1 installation (seconds)
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		253
	Raptor WD740GD		2		Dual		FastTrak S150 TX2plus		275
	Raptor WD360GD		1		Single		FastTrak S150 TX2plus		286
	Raptor WD740GD		1		Single		FastTrak S150 TX2plus		286
	Raptor WD740GD		2		RAID 0		FastTrak S150 TX2plus		298
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		309

The second example of weaker RAID 0 performance is found in a test which uses Windows Explorer to search for files that contain the word "Pentium". Here too you'd expect the hard disk perfomance to be of major importance to the results, but find out in the end that it is the processor that plays the biggest role in this part. Results of the Raptor WD740GD's are left out because the benchmark was added after the WD740GD's had been tested.

	Windows Explorer search task (seconds)
	Raptor WD360GD		1		Single		FastTrak S150 TX2plus		87,6
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		94,6
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		100,4

But the "anti-RAID-club" shouldn't start celebrating their victory, because when we add a background activity to this test like copying a network file, the RAID 0-configurations immediately take revenge on the defenceless Raptor WD360GD. Whereas the search task on the single Raptor WD360GD takes almost twice as long this way, the two RAID configurations experience much less inconvenience from the extra workload. The two Raptors in RAID 0 are 34 percent slower and the MegaRAID SCSI 320-2X requires 28 percent more time to complete its tasks. Our last test proves the usefulness of RAID in situations with heavy I/O. If you want to be able to keep on working undisturbed in those kind of situations, RAID is a blessing.

	Windows Explorer search task+ netwerk file copy (seconds)
	Raptor WD360GD		2		RAID 0		FastTrak S150 TX2plus		127,2
	Atlas 15K		4		RAID 5		MegaRAID SCSI 320-2X		127,7
	Raptor WD360GD		1		Single		FastTrak S150 TX2plus		168,6