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Expand the EXAMPLES section for atacontrol.8

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PR:		docs/117310
Submitted by:	Ted Mittelstaedt <tedm at ipinc dot net>
		with minor modifications by me.
This commit is contained in:
Remko Lodder 2007-11-28 21:37:25 +00:00
parent 4f744c0454
commit 32e1f3ed33
1 changed files with 105 additions and 1 deletions
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@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd August 16, 2005
.Dd November 28, 2007
.Dt ATACONTROL 8
.Os
.Sh NAME
@ -221,6 +221,110 @@ for example:
The new modes are set as soon as the
.Nm
command returns.
.Pp
The atacontrol command can also be used to create purely software
RAID arrays in systems that do NOT have a "real" hardware RAID card
such as a Highpoint or Promise card.
A common scenario is a 1U server such as the HP DL320 G4 or G5.
These servers contain a SATA controller that has 2 channels that can
contain 2 disks per channel, but the servers are wired to only place
a single SATA drive on each channel.
These servers do have a "pseudo" RAID BIOS but it uses a proprietary
format that is not compatible with the ata driver, and thus their
RAID bios must be switched off.
Another common scenario would be a Promise UDMA100 controller card
that did not contain the Fasttrack RAID BIOS, but did contain 2
UDMA channels.
1 disk would be attached to one channel and the other disk would be
attached to the other channel.
It is NOT recommended to create such arrays on a primary/secondary
pair on a SINGLE channel since the throughput of the mirror would be
severely compromised, the ability to rebuild the array in the event
of a disk failure would be greatly complicated, and if a disk
controller electronics failed it could wedge the channel and take
both disks in the mirror offline.
(which would defeat the purpose of having a mirror in the first place)
.Pp
A quick and dirty way to create such a mirrored array on a new
system is to boot off the FreeBSD install CD, do a minimal scratch
install, abort out of the post install questions, and at the command
line issue the command:
.Pp
.Dl "atacontrol create RAID1 ad4 ad6"
.Pp
then immediately issue a reboot and boot from the installation CD
again, and during the installation, you will now see "ar0" listed
as a disk to install on, and install on that instead of ad4, ad6, etc.
.Pp
To get information about the status of a RAID array in the system
use the command line:
.Pp
.Dl "atacontrol status ar0"
.Pp
A typical output showing good health on a RAID array might be as
follows:
.Pp
.Dl "ar0: ATA RAID1 subdisks: ad4 ad6 status: READY"
.Pp
If a disk drive in a RAID1 array dies the system will mark the disk
in a DOWN state and change the array status to DEGRADED.
This can ALSO happen in rare instances due to a power fluctuation or
other event causing the system to not shutdown properly.
In that case the output will look like the following:
.Pp
.Dl "ar0: ATA RAID1 subdisks: ad4 DOWN status: DEGRADED"
.Pp
For a mirrored RAID1 system the server WILL ALLOW you to remove a
dead SATA disk drive (if the drive is in a hot-swap tray) without
freezing up the system, so you can remove the disk and while you are
obtaining a replacement the server can run from the active disk.
The only caveat is that if the active disk is ad6, the system most
likely will NOT be able to be rebooted since most systems only
support booting from the first disk drive.
.Pp
To deactivate the DOWN disk ad6 to allow for it to be ejected, use
the following:
.Pp
.Dl "atacontrol detach ata3"
.Pp
then eject or remove the disk.
Note that this only works if the 2 disks in the mirror are on separate
channels (which is the standard setup for 1-U servers like the HP DL320).
When the new disk drive is obtained, make sure it is blank, then shut
the system down.
At this point, if the system has a RAID array card like a Highpoint or
Promise controller, you may then boot it into the BIOS of the card and use
the manufacturers RAID array rebuild utilities to rebuild the array.
.Pp
If the system has a pure software array and is not using a "real" ATA
RAID controller, then shut the system down, make sure that the disk
that was still working is moved to the bootable position (channel 0
or whatever the BIOS allows the system to boot from) and the blank disk
is placed in the secondary position, then boot the system into
single-user mode and issue the command:
.Pp
.Dl "atacontrol addspare ar0 ad6"
.Dl "atacontrol rebuild ar0"
.Pp
If the disk drive did NOT fail and the RAID array became unmirrored due
to a software glitch or improper shutdown, then a slightly different
process must be followed.
Begin by issuing the detach command (this shows the detach for disk ad6,
the primary master on channel 3):
.Pp
.Dl "atacontrol detach ata3"
.Pp
then reboot the system into single-user mode.
(don't just init the system, reboot it so that both disks get probed)
You will probably see TWO mirrored RAID arrays appear during the boot
messages, ar0 and ar1.
Issue the command:
.Pp
.Dl "atacontrol delete ar1"
.Dl "atacontrol addspare ar0 ad6"
.Pp
Now a status command will show the array rebuilding.
.Pp
.Sh SEE ALSO
.Xr ata 4
.Sh HISTORY