kern/121481: [gmirror] data rot on disk with gmirror

[Steiner, Bernard]

The following reply was made to PR kern/121481; it has been noted by GNATS.

From: "Steiner, Bernard" <Bernard.Steiner at lahmeyer.de>
To: "Dan Naumov" <dan.naumov at gmail.com>, <bug-followup at FreeBSD.org>
Cc:  
Subject: RE: kern/121481: [gmirror] data rot on disk with gmirror
Date: Mon, 13 Jul 2009 10:50:02 +0200

 Dan,
 
 > RAID offers protection against very specific kinds of disk 
 > failure and does not offer any kind of protection against bit 
 > rot. I want to emphasize that this is not a FreeBSD issue, 
 > but a RAID issue in general and you will run into exact same 
 > limitations if you try raid on Linux or Windows or hardware
 
 I was asking for -w to be implemented by gmirror, and/or graid6
 (double parity) be implemented (also with -w or even -w2 ;-)
 
 > raid from any hardware vendor. For another example of a fault 
 > that RAID mirror will NOT protect you or even warn you 
 > against, is your disk/raid controller going berserk and 
 > writing garbage to the mirror or one of it's member disks.
 
 ACK. This is exactly why I want a check on the data read.
 
 > [checksumming utilities]
 
 Please explain how to do that on both sides of a gmirror.
 AFAIK, gmirror can be configured in the following ways:
 (1) always read from "primary" disk => cannot check secondary
 (2) round robin or load => read cannot be reliably reproduced
 
 Correct me if I am wrong, but this does not seem like a solution
 to my problem.
 
 > [ZFS / Solaris]
 
 I think I *like* ZFS (raidz2) and probably go with that.
 Solaris' future is uncertain in the light of SUN's future...
 
 I think maybe I'll wait a while till the warning is edited out
 of ZFS in FreeBSD and give it another shot.
 
 Bernard
 
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