Promise VTrak J300s

Test results - Read Performance

100% Sequential Reads

100% Sequential Read Performance (MB/Sec)
	1 DQL/Disk	2 DQL/Disk	3 DQL/Disk
SAS	536 MB/sec	536 MB/sec	540 MB/sec
SATA II	370 MB/sec	374 MB/sec	407 MB/sec
SATA I	356 MB/sec	333 MB/sec	348 MB/sec
SCSI	129 MB/sec	128 MB/sec	126 MB/sec

When we first gathered the test data together, we were very impressed with the results. Both SAS and SATA I/II show extremely high performance with 100% sequential accesses. The SCSI and SAS drives are similar in terms of capacity while the SAS drives offer higher rotational speeds. Meanwhile, the SATA drives are all 7200 RPM models, theoretically offering less performance but higher capacities than either of the other two solutions.

We can really see the benefit a point-to-point architecture has to offer, as well as the impact the shared bus has on performance. All of the SAS/SATA solutions offer much higher read performance than the SCSI offering here, which helps to explain why SAS solutions are rapidly increasing market share. SCSI Ultra320 can't even come near its theoretical 320 MB/s transfer rates due to sharing overhead. Strangely, we see SCSI and SATA I drop slightly as the DQL increases, while SAS and SATA II increase slightly.

It is interesting to note the performance at low Disk Queue Length between the different technologies. Both SAS and SCSI are very close to their peak performance even at a DQL of 2, whereas SATA needs a DQL of 4 before it starts performing well. As the Disk Queue Length increases, both SAS and SCSI hold their performance well, and a gap starts to emerge between SATA I and SATA II.

95% Sequential Reads

95% Sequential Read Performance (MB/Sec)
	1 DQL/Disk	2 DQL/Disk	3 DQL/Disk
SAS	254 MB/sec	323 MB/sec	356 MB/sec
SATA II	138 MB/sec	178 MB/sec	194 MB/sec
SATA I	132 MB/sec	167 MB/sec	182 MB/sec
SCSI	93 MB/sec	119 MB/sec	126 MB/sec

Here we start to see the impact that randomness has on our read performance. SAS is still in the lead but SCSI is starting to catch up to SATA I/II. The higher rotational speeds of SCSI and SAS solutions can help relative to most SATA offerings, as access times depend in part on rotational latency. Performance continues to grow through the whole range of Disk Queue Length with SAS breaking 350MB/sec around 34. This is significantly higher then the 175-200MB/Sec of SATA I/II and 125MB/Sec that SCSI is able to obtain.

Again, we see the benefit that the point-to-point architecture has to offer over the old shared bus architecture. SATA II maintains a slight lead over SATA I, but both don't even come close to touching SAS. SCSI gains ground, but given the maximum throughput of around 130 MB/s that was measured in the 100% sequential test, it still trails by a large margin in this workload.

80% Sequential Reads

80% Sequential Read Performance (MB/Sec)
	1 DQL/Disk	2 DQL/Disk	3 DQL/Disk
SAS	144 MB/sec	188 MB/sec	210 MB/sec
SATA II	75 MB/sec	96 MB/sec	103 MB/sec
SATA I	74 MB/sec	96 MB/sec	102 MB/sec
SCSI	77 MB/sec	104 MB/sec	115 MB/sec

At 20% Random Reads we start to see SATA I/II losing its performance advantage over SCSI, while SAS clearly remains as the performance leader. We continue to see performance grow as the DQL increases, but it's interesting to see that SAS is ramping up faster then everyone else. SATA I and SATA II are struggling to keep up with SCSI which has now moved into second place. At this point, the performance of SATA I and SATA II are almost identical.

Random (0% Sequential) Reads

Random Read Performance (MB/Sec)
	1 DQL/Disk	2 DQL/Disk	3 DQL/Disk
SAS	113 MB/sec	165 MB/sec	197 MB/sec
SATA II	43 MB/sec	53 MB/sec	56 MB/sec
SATA I	43 MB/sec	53 MB/sec	55 MB/sec
SCSI	70 MB/sec	100 MB/sec	112 MB/sec

In the previous graphs we've seen the impact that random data has on our overall throughput. Now that we are at 100% Random accesses, we get to see how the drives perform in a 'worst-case' scenario. SAS continues to take the performance lead by throughput that's almost double that of SCSI, but now SCSI is almost twice as fast as SATA I/II. Looking at the results through the whole DQL range, SAS continues to grow without showing signs of slowing down, whereas SCSI and SATA I/II appear to level off around 32-36 DQL.

While a point-to-point architecture clearly has advantages with sequential accesses, there is still something to be said about spindle speed and disk firmware. However, given that SCSI maxed out at ~130 MB/s in the sequential testing, higher spindle speeds would only go so far in closing the gap between SCSI and SAS. SATA drives like Western Digital's 10K RPM Raptor should also be able to close the distance with SCSI in highly random usage scenarios.

We've covered the read performance, but what happens when we test writes?