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Mixing HD spindle speeds and how to prioritise?

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I played about with UNRAID a year or so ago and had to tear the server down to free up the CPU for my kid's 'learn from home' computer. Now I'm sorting out how to rebuild it with what I've managed to cobble together: Three 4TB shucked WD Elements USB drives, which I believe are 5400rpm and a single 7200rpm Toshiba NAS N300 4TB. These are barely used and roughly 12 months old. I'll also have a 500 GB SSD for the cache drive.


So how to prioritise the better quality NAS drive? Make it the Parity drive? Or something else?


Obviously what's underlying this question is which drive is being asked to work the hardest in an array? The Parity or the one that stores most of my family media files? Possibly the drive that I automate backing up family boot volumes to since these will be written to (in theory) more frequently than a media drive which will only be read from once the media is written.





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Basically, it does not make much difference.  The slowest drive will determine what the speed of array operations (parity checking, parity rebuild, disk rebuild, ect.).  Reading of data is usually restricted to the speed of the network.  (Read and Write speeds of the array are not symmetrical with Unraid.)  If you are writing directly to the array, the spindle speed will matter. (However, you only have one 7200 disk, that point is mute.)  However, you are using an SSD and I assume that you will use it to cache writes after you have done the initial data load so the final write speed to the array is not a big concern from a user standpoint.


Oh, one more thing.  While I haven't looked at the latest data from Backblaze, there is not  much evidence that 'NAS' drives are any more reliable than standard consumer drives.  In some cases they do have different firmware, but this does not seem to make them last longer or work more reliably in day-to-day Unraid usage.  

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It is my belief that manufacturers are using the discount prices on USB Enclosures as a way to move excess drive inventory off of their books.  That is to say, they are getting rid of drives that they can't sell any other way.  The buyer never knows what model of drive is inside of that enclosure until he cracks it open. 

Edited by Frank1940
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