From mboxrd@z Thu Jan  1 00:00:00 1970
From: Phil Turmel <philip@turmel.org>
Subject: Re: proactive disk replacement
Date: Tue, 21 Mar 2017 12:55:44 -0400
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To: David Brown <david.brown@hesbynett.no>, Reindl Harald <h.reindl@thelounge.net>, Jeff Allison <jeff.allison@allygray.2y.net>, Adam Goryachev <mailinglists@websitemanagers.com.au>
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On 03/21/2017 09:02 AM, David Brown wrote:

> With RAID6 (or three-disk RAID1), you can tolerate /two/ URE's on
> the same stripe.  If you have failed a disk for replacement, you can 
> tolerate one URE.

One nit to pick here:  The UREs have to be in the same 4k block/sector,
not just in the same stripe.  The stripe cache and all parity
calculations are done on strips of 4k blocks, not whole N*chunk stripes.

That makes the odds even larger.

Phil