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For a consumer desktop system, which setup of SSDs would be more reliable over the course of months?

  1. A single disk that offers TRIM and/or utilites for maintaining it - e.g. The Intel SSD Toolbox.
  2. A RAID of two less reliable disks in a mirror, with the TRIM/Toolbox not being usable through the RAID controller.

A single, reliable disk or a mirror of less reliable disks?

Anecdote: I'm trying to decide between keeping the two OCZ Vertex Plus's that I have in a mirror (They get miserable reviews for reliability) or going for an Intel branded one (Which have good reliability stats).

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2 Answers 2

up vote 2 down vote accepted

TRIM does not affect the reliability at all, though obviously it is an extremely useful feature to have.

It's possible that each of your two unreliable drives are so unreliable that you'd be better off with a single more reliable drive, though this is unlikely. Let's assume that your reliable drive has a chance of failure of 1% over the course of a year, while your odds of failure of the less reliable drives are 20%. Further, let's assume that the two less reliable drives would fail in a statistically uncorrelated manner. And once one drive fails, you will replace it and rebuild your array within 24 hours.

Your odds of failure using the more reliable drive are then 1%. Your odds of losing at least one of the less reliable drives are approximately 36%. If you lose a single drive, though, you don't care unless the second drive fails within 24 hours. The odds of that happening are approximately 0.00055%. I calculated this by doing 20% / 365. I believe my math is correct, but you'll want to double-check.

In other words, a RAID-1, assuming drive failures are uncorrelated and assuming you replace a failed drive and rebuild the array within 24 hours, is going to be far, far more reliable than a single drive. Of course, the RAID-1 controller itself can fail. Or your computer can be struck by lightning, or your house can go up in flames. Or you can delete a file you didn't mean to. Always back up your data.

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True, even OCZ's shouldn't fail that close to each other.What about which setup is more reliably performant? Wouldn't the mirror lose performance over time because of no TRIM/Maintenance? –  Bort Feb 24 '12 at 18:29
    
RAID-1 should allow faster reads (system can pick either drive), though it won't help for writes. Lacking TRIM means that the drive likely will lose performance over time. Some SSD's do background garbage collection (en.wikipedia.org/wiki/…) which helps mitigate this. –  ChrisInEdmonton Feb 24 '12 at 18:38
    
It's never amusing when you lose more drives during a rebuild from a failed drive. That was an unhappy day as we then had more work repairing and restoring from backup. –  Brian Knoblauch Feb 27 '12 at 20:11
    
I had some doubts about your answer, Chris, but my mirror of unreliable drives seems to be handling itself ok - I'll just be sure to do a verify/correct regularly and give you the checkmark. –  Bort Feb 29 '12 at 14:32
    
Bort, please please also back up your important data! Now, when everything's working well, is exactly the time you should do that. :) –  ChrisInEdmonton Feb 29 '12 at 14:49

Note: Just in case check the serials of the disks not to be close because that can result in a bad batch and that might make your raid 1 useless

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VERY important! –  Brian Knoblauch Feb 27 '12 at 20:10

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