October 23, 2025Oct 23 Yesterday, I started a parity check on my array of 16T drives to be sure it is error-free before upgrading a drive.After 3 hours, it had reached 12%. Reads from the Array drives were reported at about 250 MB/s.16,000,000 Mbytes / 250 MB/s = 17.7 hours. I'm assuming this is a physical level process, and the fact that the drives are 50% full doesn't matter.Today after 20 hours running, it is at 61%. Reads from the Array are now running around 150 MB/s.What happened? Drive temperatures have gone from 34C to 41C since yesterday. Is that hot enough to cause them to slow down to prevent overheating? Edit - now at 22 hours, speed is down to 120 MB/s, and estimate is 17 more hours to completion. If it continues to slow, it may never finish? Edited October 23, 2025Oct 23 by timg11
October 23, 2025Oct 23 Community Expert HDD speed is not constant; they are much slower as they get to the internal sectors, and if you have multiple capacity disks, the issue will be more noticeable since it will slow down when you reach the end of the smallest capacity, then speed up a little, then slow down again, and so on. Example of a typical graph:
October 23, 2025Oct 23 Author That graph looks exactly like what I observe. Thanks! (Curious about the little jump back to 250 right at the end by 100%, though)
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