FreeBSD Preferred RAID controllers

Matthew Seaman m.seaman at
Sat Feb 14 08:31:08 PST 2009

Gabe wrote:
> --- On Mon, 2/9/09, Matthew Seaman <m.seaman at> wrote:
>> From: Matthew Seaman <m.seaman at>
>> Subject: Re: FreeBSD Preferred RAID controllers
>> To: nrml at
>> Cc: freebsd-questions at
>> Date: Monday, February 9, 2009, 3:08 PM
>> Gabe wrote:
>>> Now with a gstripe+gmirror setup, would it be possible
>> to fail a
>>> specific drive on purpose? I mean fail a (good) drive,
>> pull it out,
>>> replace it and rebuild(?) it. I know I know, but humor
>> me.
>> Yes.
>> 	Cheers,
>> 	Matthew
>> Well, to 'fail' the drive, you'ld have to
>> physically pull the drive
>> from the chassis which will involve a power cycle unless
>> you've got
>> hot-swap drives.  Of course, you should confirm that your
>> system will
>> boot with the RAID in a degraded state and that rebuilding
>> the RAID will
>> continue even if interrupted by a reboot.  gmirror(8)
>> passes those
>> tests.  You do have to type some commands to get a mirror
>> to rebuild
>> (examples are shown in the man page) unlike some hardware
>> RAIDs where
>> simply inserting an unused disk is sufficient.
>> -- Dr Matthew J Seaman MA, D.Phil.                   7
>> Priory Courtyard
>>                                                  Flat 3
>> PGP:     Ramsgate
>>                                                  Kent, CT11
>> 9PW
> Hello again all,
> So I wanted to test out gmirror on software RAID so I installed a completely vanilla FBSD 7, as base an install as you can get, it hasn't even been on the network. Anyway, I did the following upon first boot to get gmirror going:
> # sysctl kern.geom.debugflags=17
> Then:
> # gmirror label -vb round-robin gm0 /dev/ad0
> Then:
> # gmirror load
> Then:
> # echo 'geom_mirror_load="YES"' >> /boot/loader.conf
> Then I edited /etc/fstab to show:
> /dev/mirror/gm0s1b    none        swap    sw              0       0
> /dev/mirror/gm0s1a    /           ufs     rw              1       1
> /dev/mirror/gm0s1e    /tmp        ufs rw      0   0
> /dev/mirror/gm0s1f    /usr        ufs rw      2   2
> /dev/mirror/gm0s1d    /var        ufs     rw              2       2
> I then rebooted the system, once I setup the mirror:
> # gmirror insert gm0 /dev/ad1
> # gmirror status
> and it shows as COMPLETE. Okay, here comes the annoying part, I've got hot-swappable bays and I went ahead and pulled the drive. I then tried to write to the disk so that it realizes the disk is no longer there:
> # touch file
> once I do that and execute: gmirror status it shows as degraded. All fine and dandy. However when it comes time to pop the drive back in the drive is not recognized at all. I mean, the green light on the bay comes on so it definitely makes a connection but then thats it, atacontrol list doesn't list it and gmirror status still shows the same, degraded.
> What gives? I wonder if this is hardware related? Bios related even? Any clues?

See atacontrol(8)

   # atacontrol list

shows what your system knows is there

   # atacontrol attach X

where X is the channel number, probes and attaches any devices on that
channel in exactly the same way it is done at system boot.

See camcontrol(8) if you've got SCSI drives.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
                                                  Kent, CT11 9PW

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