RAID controllers without cache (or with cache disabled) force additional I/O to wait until the previous I/O is completed. Additionally, RAID functionality incurs significant overhead due to the data protection features. WRITE I/Os must be accompanied by several READ I/Os, in addition to redundancy calculations (Parity or Mirroring). RAID 5 writes incur the most overhead due to the need to perform reads from every drive multiple times before the write is completed.
Without cache, the write performance of an array may fall to speeds that are less than the write performance of a standard SATA port (approximately 30MB/s). Enabling the write cache of the hard drives (Disk Cache Policy) may increase write performance, but also increases the risk of data loss in the event of power fluctuation/loss.
RAID controllers with cache (H730(P),H710(P), H700, PERC 6, PERC 5, etc.) are able to buffer large amounts of I/O operations which can be calculated and written to the applicable disks at a later time. RAID 5 performance can typically be in the 100-150MB/s range (or higher) for a controller with cache depending on how many drives are in the array.
It is important to note that performance results vary widely depending on many factors. Usage of the array (bandwidth, writes, reads) can have a major impact on the overall performance. For example, when using an H310 controller, performance may be satisfactory when usage is low. As usage increases to the maximum bandwidth threshold of the controller however, performance may drop dramatically. Upgrading to a faster controller with cache will almost universally improve performance substantially across all spectrums of usage and demand.
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Identyfikator artykułu: SLN164091
Data ostatniej modyfikacji: 10/23/2019 08:34 AM
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