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

[Dan Naumov]

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

From: Dan Naumov <dan.naumov at gmail.com>
To: bug-followup at FreeBSD.org, zdbs at lif.de
Cc:  
Subject: Re: kern/121481: [gmirror] data rot on disk with gmirror
Date: Mon, 13 Jul 2009 11:23:32 +0300

 Bernard, while I understand your frustration, you are barking up the wrong tree.
 
 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 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.
 
 If you are happy with just getting a warning when file(s) somewhere
 are silently getting corrupted, this can easily be easily implemented
 with existing tools: there are plenty of checksumming utilities you
 can use to checksum your datasets and you could set up a cronjob to
 have the utility run a check of your files against a known hash
 database and list all the files (if any) that have changed, mailing
 you the output. When properly configured, this can also help with
 intrusion detection, as it can help detecting all new or changed files
 on the system :)
 
 However, if you require not only a warning, but also automatic
 recovery and healing from such corruption, your only option is ZFS and
 if you have evaluated the state of ZFS in FreeBSD and concluded that
 it's not mature enough for your needs, then your only other option is
 Solaris.
 
 - Sincerely,
 Dan Naumov