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?

Test configuration Test results – Write Performance
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  • JarredWalton - Monday, February 5, 2007 - link

    "or seek times" = "where seek times"
  • yyrkoon - Saturday, February 3, 2007 - link

    many 'old timers' are going to claim SCSI is better than anything, because its been around a long time, and has a proven track record. What these 'old timers' don't realize, is that SAS, and SCSI drives, share the same ancestry, except that SAS, also shares a history with SATA. *shrug*
  • mino - Sunday, February 4, 2007 - link

    Yes they are those.
    However most posters here do NOT dispute the benefits and superiority os SAS over U320.
    The point is that according the numbers published even SATA 7.2k is on par with SCSI320 10k !!!
    Those numbers simply coudn't be much more away from the reality then they are.

    Artificially more than halving the performance of a tested platform simply is not acceptable.

    Also to make tables in the sense SATAI vs. SATAII vs. SCSI vs. SAS is on itself seriously misleading to the extent that best thing to do for AT (provided they were not paid for it!) would be to call in the article eithe indefinitelly or for rewrite.

    Actually the reality is:
    SATA I or SATA II driver do not exist, there are only SATA drives inn existence as of now.
    performance-wise on single to 6-drives/system:
    SATA(7.2k) < SATA(10k) < SCSI(10k) = SAS(10k) < SCSI(15k) = SAS(15k)
    on 8+drives system:
    SATA(7.2k) < SATA(10k) < SCSI(10k) < SAS(10k) < SCSI(15k) < SAS(15k)

    For an 12-drive test the results should be:
    SATA(7k) << SCSI(10k) << SAS(15k) which is obvious even before any testing.

    However much more beneficial test would be:
    SATA(10k-Raptor) vs. SCSI(10k) vs. SAS (10k) with SCSI and SAS driver ideally from the same line.
  • mino - Sunday, February 4, 2007 - link

    "SATA I or SATA II driver" --> "SATA I or SATA II drives"
  • mino - Saturday, February 3, 2007 - link

    Yes, one sometimes has to make compromises.
    But benchmarking SCSI setup with 12drives on a SINGLE cable is plain stupid and tabloid-like aproach.
    This organization seriously criples perfromance and is NEVER used unless there is some very serious reason for it.
  • mino - Saturday, February 3, 2007 - link

    If you did have no SCSI option than the one you used, you should not have published those "SCSI" numbers at all. Those numbers as they are have nothing to do with SCSI being poor, they are simply showcasing that 3yrs 10k drive are slower than new 15k drives. Nothing new here.
  • Googer - Friday, February 2, 2007 - link

    That chart is missing the old 5.25 inch drives. The most famous of those was probably the Quantum Bigfoot. Quantum was bought out by Maxtor.

    http://images.anandtech.com/reviews/it/2007/promis...">http://images.anandtech.com/reviews/it/.../promise...

    http://www.pcguide.com/ref/hdd/op/formIn525-c.html">http://www.pcguide.com/ref/hdd/op/formIn525-c.html
  • Justin Case - Friday, February 2, 2007 - link

    Maybe the article author should read this...

    http://www.sata-io.org/namingguidelines.asp">http://www.sata-io.org/namingguidelines.asp
  • monsoon - Friday, February 2, 2007 - link

    Hello,

    I'm used to change computers frequently, I have lots of data to store.
    Currently I've got 4 external 300Gb drives and 4 external 400Gb drive; all of them connected through firewire.

    I've been looking eagerly for solutions similar to the NORCO DS-1220; but I need to connect the storage unit to laptops as well, so it has to control RAID5 all by itself.

    I can't find alternatives in the market, and while the UNRAID solution looks interesting, it's not safe, neither easy to implement.

    Looking forward to external storage devices reviews for home users with big archives.
    Units need to stand the test of time and be there while PCs come and go.
    Ideally, I must be able to replace drives with higher capacity when they get cheaper, without having to replace all of them at the same time.

    It better be silent; well, at least not loud...

    Any idea ?

    Thanks
  • mino - Saturday, February 3, 2007 - link

    Look for some reliable NAS solution (+Gbit swith - now dirt cheap).

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