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Building new home server with RAID 5    Building/Modding/ Overclocking

Started 12/4/17 by Joe PC User (JoePCUser); 382 views.



Fricking add pass-thrus...

These bad boys:
There, that should cover the 4 links I gave you, in-order.

I'd give you pointers to SAS SSDs, but their pricing is TOTALLY out of whack.
  • Edited December 6, 2017 6:59 pm  by  THECOM

From: xSomeguyx


I think the commentary on RAID 5 is correct; with BIG drives, rebuild time for a gigantic array is extensive, and is more prone to completely borking since you're taxing the other disks.  I do think that it's overstated though; I've rebuilt RAID 6 arrays (same as RAID 5, but instead of one parity drive there are two) with 12 disks a number of times, and though it's not fast it does succeed.  I'm a big fan of RAID 10 though, especially if you can sacrifice the disk space; the speed boost is real nice, especially when you're talking about writes.

The problem isn't the RAID5 itself.  It's the size of the disks themselves vs the overall number of disks in the raid.
With a 12 disk RAID, you're spreading out your data MUCH further than you are with a 3 drive RAID.  And with double-parity, you have more recovery chances.
With a 4TB drive, the URE rate is something like 10^14.  This gives you an almost guaranteed error at 12.5TB (3 plus a bit) complete read cycles of the array.

Since your RAID is still, only 8TB, your chances of tripping a URE aren't terrible.  The more drives you add, and the more parity stripes you add, the better your chances of not hitting a truly unrecoverable error.

But, with 6, 8 and even the newer 10+TB drives, your chances of tripping a URE are STILL only about 10^14 (some better drives are 10^15, giving you a bigger margin of safety).
Why are these figures not improving with the improvements in tech?  Because the areal density of the drives keep going up.
So, essentially, they're the same mechanism, they're just cramming more into the same space.

  • Edited December 8, 2017 6:50 pm  by  THECOM