What is the rule of thumb in performance characteristics and differences between 7200rpm (SATA/SAS) and 15000rpm (SAS) hard disc drives of the same generation?
HDD: performance differences between 7.2k SATA and 15k SAS
performancesassata
performancesassata
What is the rule of thumb in performance characteristics and differences between 7200rpm (SATA/SAS) and 15000rpm (SAS) hard disc drives of the same generation?
Best Answer
It's a case of math. I/O-per-second is determined by the following calculation:
Random I/O = 1000/ (average latency + seek time)
For a 7.2K RPM drive, a seek-time of 8.5ms and latency of 4.16 gives an IOPS number of 78.
For a 15K RPM drive, a seek-time of 2.6ms and latency of 2.0ms gives an IOPS number of 217 .
For a 15K RPM drive, a seek-time of 3.4ms and latency of 2.0ms gives an IOPS number of 185.
These are just examples based on a selection of current (as of this writing) drives from Seagate.
Interface (SAS vs SATA) doesn't impact these numbers meaningfully. The RPMs are what determine the performance. Sequential I/O performance is a different number, but most server I/O these days is significantly random.
As you can see, the performance difference between the two tiers of speed can be quite significant.