Performance of server disks with SSD caching
We tested several configurations of disk arrays that are suitable for use in servers.
We tested the following configurations:
- 4 x 300GB SAS2 10K + RAID10 on a PCI-E 2.0 controller (Reference 4 x 300GB RAID10)
- PCI-E SSD 120GB MLC (Inexpensive PCI-E SSD 120GB)
- 2 x SSD 120GB MLC + RAID0 on a PCI-E 2.0 controller with optimized firmware (Inexpensive 2 х SSD 120GB RAID0)
- 4 x 300GB SAS2 10K + RAID10 on a PCI-E 2.0 controller + SSD MLC 120GB caching I/O (Hybrid 4 x 300GB RAID10 + SSD caching)
The method of comparisonIn all tests, we used a server with Microsoft Windows 2008 R2 Enterprise. Performance tested synthetic test Iometer. In comparison, used performance for random read / write blocks of 4KB. It is also estimated the cost of a single I/O operation per second and the cost per GB of usable capacity drives (including the controller).
The graph shows that the use of SSD in any form, rate increases sharply IOPS, which is quite natural. But apart from this reduced the price of one I / O operations per second, and remains low regardless of the type of access to the SSD. If we consider the index price per gigabyte of usable capacity, we see a clear advantage SSD caching. Along with the fact that this system showed the maximum rate IOPS, so also the cost per gigabyte was slightly higher than the conventional disk array. It is also reflected in the chart that the use of a discrete RAID-controller only to realize that a stripe of two SSD - not a budget option.
Operations on random write option was the most productive of the two RAID0 SSD, but it also proved to be the most expensive. Also, be aware that the cost of the solution will have to double to provide fault tolerance with the transition to RAID10. The hybrid array with SSD-caching showed the optimal result for all indicators.
When streaming read operations, as we see ordinary disk array wins for all indicators.
ResultsOf course, performance may vary depending on the size of blocks or disks in the array. Just keep in mind that in real applications, in some cases require absolute performance rather than relative price.
But in any case, the use of SSD caching can significantly improve performance I/O operations per second for server disk arrays.
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