One slow drive in an array of four identical drives

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Is the drive out of spec? Is it possible the other 3 are just lottery winners whereas the one "slower" drive is actually closer to the documented specs?
Anybody have any ideas what could be wrong? (I don't think it's vibration. But I'll check.)
Vibration is worth checking and ruling out. We know that modern drives have become increasingly sensitive to vibration.

What you might try, is using the options for displaying increased breakdown of timing during each large 1GB read.

The Benchmark is transferring 32,768 sectors at a time (since we learned earlier that some drives fail to meet the spec of transferring 65,536 sectors and it wasn't worth the trouble of determining each drive's upper limit. 1GB is 2,097,152 sectors. So at 32,768 sectors per transfer, we need to request 64 transfers.

Adding a /1 after “RS” provides a scaling of x1 — So the effective performance of each of those 64 blocks is broken out and shown.

Adding a /2 forces a 2x scaling. So the block size is cut in half and twice the blocks are transferred. This has the effect of providing twice the granularity of transfer and individual block display.

A /3 forces another factor of two, so 4x scaling and 4 times the number of blocks.

And /4 forces 8x scaling. So we transfer 512 blocks of 4,096 sectors.
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It may be just a firmware update on the 3 faster drives. the manufacturer is always tweaking the drives they manufacture, to get every last bit of speed out of them, and you *may* be able to speed up the slow drive with a firmware update, to bring it up to where the other 3 are...(worth a check).
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