I/O Meter Performance - SSD versus Enterprise SAS and SATA disks

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I/O Meter Performance

IOMeter is an open source (originally developed by Intel) tool that can measure I/O performance in almost any way you can imagine. You can test random or sequential accesses (or a combination of the two), read or write operations (or a combination of the two), in blocks from a few KB to several MB. Whatever the goal, IOMeter can generate a workload and measure how fast the I/O system performs.

First, we evaluate the best scenario a magnetic disk can dream of: purely sequential access to a 20GB file. We are forced to use a relatively small file as our SLC SSD drives are only 32GB. Again, that's the best scenario imaginable for our magnetic disks, as we use only the outer tracks that have the most sectors and thus the highest sustained transfer rates.

IOMeter Sequential Read

The Intel SLC SSD delivers more than it promised: we measure 266 MB/s instead of the promised 250 MB/s. Still, purely sequential loads do not make the expensive and small SSD disks attractive: it takes only two SAS disks or four SATA disks to match one SLC SSD. As the SAS disks are 10 times larger and the SATA drives 30 times, it is unlikely that we'll see a video streaming fileserver using SSDs any time soon.

Our Adaptec controller is clearly not taking full advantage of the SLC SSD's bandwidth: we only see a very small improvement going from four to eight disks. We assume that this is a SATA related issue, as eight SAS disks have no trouble reaching almost 1GB/s. This is the first sign of a RAID controller bottleneck. However, you can hardly blame Adaptec for not focusing on reaching the highest transfer rates with RAID 0: it is a very rare scenario in a business environment. Few people use a completely unsafe eight drive RAID 0 set and it is only now that there are disks capable of transferring 250 MB/s and more.

The 16 SATA disks reach the highest transfer rate with two of our Adaptec controllers. To investigate the impact of the RAID controller a bit further, we attached four of our SLC drives to one Adaptec controller and four on another one. First is a picture of the setup, and then the results.


IOMeter Sequential Read, 2 versus 1 RAID controllers

The results are quite amazing: performance improves more than 60% with four SSDs on two controllers compared to eight X25-E SSDs on one controller. We end up with a RAID system that is capable of transferring 1.2GB/s.

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