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Sequential Read & Write Patterns

IOMeter is sending a stream of read and write requests with a request queue depth of 4. The size of the requested data block is changed each minute, so that we could see the dependence of the disk subsystem’s sequential read/write speed on the size of the data block. This test is indicative of the maximum speed the disk subsystem can achieve.

All the controllers, save for the 3ware (whose performance is affected by its specific architecture), deliver about the same top speed but reach it on different data blocks. The Areca and HighPoint reach their maximum speed on 16KB data blocks. The LSI does the same on 64KB data blocks and the Adaptec, on 128KB blocks. The Promise needs 512KB blocks (a full stripe with 64KB for each of the eight disks) to show its top speed.

Sequential reading from RAID10 shows the controllers’ ability to parallel read requests to the two disks of a mirror pair. None of them behaves ideally, but the Areca is obviously better and faster than the others (and it delivers the same performance irrespective of the amount of onboard memory). The Areca is also in the lead in terms of reading small-size data chunks. The Adaptec and HighPoint are good, too, but the latter is too capricious about the size of the data chunk. The Promise, LSI and 3ware have disappointing results in this test.

The standings do not change when it comes to reading from RAID5 and RAID6. The Areca and HighPoint are as good at sequential reading as the Adaptec was at random writing.

The 3ware is quite a disappointment. Its top speed is lower than that of the other controllers. It is rather slow with small data chunks and has big problems with large data chunks.

The HighPoint is in the lead when writing to RAID0. The Areca follows the leader closely in the 512MB version but falls behind in the 2GB version. We can’t explain this. The same problem plagues the Adaptec which has such a low speed of writing as if it worked with a single disk rather than a RAID array.

The 2GB Areca has the same problems when writing to RAID10. The Adaptec behaves oddly. It is the best of the average-performance controllers on small data blocks and is the overall best in terms of top speed. However, it has an inexplicable performance hit on 128KB data blocks. The 512MB Areca looks best overall. It has excellent results on small blocks and a very stable and high speed with large ones. The HighPoint falls behind, again. It has problems with large data blocks.

Few controllers can deliver a high speed of sequential writing to RAID5. Good results only come from the Areca (in the 512MB version as its 2GB version has problems again) and HighPoint. The LSI and 3ware are much slower than the leaders while the Adaptec has some problems again. The Promise only gets some speed on 128KB data chunks.

The RAID6 results are similar to the RAID5 ones, so we will only point out a few main differences. The Areca works well in both versions now. The HighPoint slows down on large data blocks and the LSI has huge problems there, too. The Adaptec and Promise still show depressing results. And while the low performance of the Promise is explained by its turned-off deferred writing, we can find no explanation for the Adaptec.

 
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