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From: Sandy Rutherford <sandy@krvarr.bc.ca>
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Date: Sun, 19 Jun 2005 22:52:25 -0700
To: Alex Zbyslaw <xfb52@dial.pipex.com>
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Cc: "P.U.Kruppa" <root@pukruppa.de>, freebsd-questions@freebsd.org
Subject: Re: Yet another RAID Question (YARQ)
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>>>>> On Sun, 19 Jun 2005 12:28:14 +0100, 
>>>>> Alex Zbyslaw <xfb52@dial.pipex.com> said:

 > A word of caution, though.  A Linux system (which I help administer) had 
 > two SCSI disks mounted as RAID-1 through some kind of Adaptec 
 > controller.  Recently the machine crashed and it transpires that one of 
 > the disks hadn't been written to since 2002!  I am told that the bootup 
 > screen showed the RAID-1 as working, and Linux could *only* see one 
 > virtual disk -- the supposed RAID mirror.  So, I think your question is 
 > a very good one!  We had (apparently) no way of knowing what was going 
 > on. The machine crashed with no messages whatsoever, after losing all 
 > access to its disks, and there was no indication that RAID-1 was not 
 > functioning.

In order to boost read performance, a RAID card should interleave
reading from a RAID-1 volume by reading alternately from one drive and
then the other.  You can see this in alternate blinking of the
activity lights of the drives.  If you are not seeing this when
copying a large file, then this would suggest that a RAID-1 volume is
not working as it should.

Sandy