August 7, 20223 yr Hi, I've been using UnRAID for some years, my server contains 24 different sized HDDs, although all my HDDs can read/write sustainably at over 120MB/s, some even over 250MB/s, I have never seen the speed over 90MB/s during daily use, its usually like 50~80MB/s. The only time when the HDDs read/write at full speed is during the parity check. While checking the system info, I've noticed the P+Q algorithm is like 19599 MB/s + 35330 MB/s, I assume there'd be no problem with the CPU power. What is the main cause that slows down the HDDs read/write speed?
August 7, 20223 yr Community Expert Read speed should be the maximum disk read speed at that point, note that disks are much faster in the outer sectors compared to the inner ones. Write speeds can be much faster, assuming no controller bottlenecks, if you use turbo write, at the expanse of all disks spinning up for writes.
August 7, 20223 yr Author 18 minutes ago, JorgeB said: Read speed should be the maximum disk read speed at that point, note that disks are much faster in the outer sectors compared to the inner ones. Write speeds can be much faster, assuming no controller bottlenecks, if you use turbo write, at the expanse of all disks spinning up for writes. But why the speed isn't as fast as expected (up to 120MB/s) ? I've tried to transfer very large files from one disk to another, it starts at full speed (maybe because of the cache pool ?), but after a few giga bytes, it slows down to some 80MB/s.
August 7, 20223 yr Community Expert 36 minutes ago, georgez said: I've tried to transfer very large files from one disk to another Array disk to array disk will never be fast because of parity, I was referring to reads and writes from the array to another computer.
August 7, 20223 yr Author 8 hours ago, JorgeB said: Array disk to array disk will never be fast because of parity That’s exactly what confuses me, I guess parity calculation is based on P+Q algorithm, since the P+Q algorithms are very fast in my case, why the parity related operations so slow?
August 7, 20223 yr Community Expert Solution 1 minute ago, georgez said: That’s exactly what confuses me, I guess parity calculation is based on P+Q algorithm, since the P+Q algorithms are very fast in my case, why the parity related operations so slow? It is not the time to calculate the parity that is the issue, but the disk rotations involved. This is described here in the online documentations accessible via the ‘Manual’ link at the bottom of the GUI.
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