Zulus Tips

Since 5.3-Release, FreeBSD has gmirror utility, which allows you create software RAID1. So if you have some low-end server and you need some redundancy - gmirror is right choice.

RAID1 creation process is _very simple_ and completely described in gmirror(8) man page, but i will post small how-to here.

First of all you need check that you have two identical drives. Second drive may be bigger, but total array size = smaller drive size. You can create RAID1 using this command:

Where gm0 is array name, /dev/ad4 is first drive. If you get this message “Can’t store metadata on /dev/da4: Operation not permitted” you need to set sysctl value kern.geom.debugflags to 16:

sysctl kern.geom.debugflags=16

Next you need make backup copy of your current /etc/fstab. After this open fstab in your favorite text editor and change all /dev/ad4 to /dev/mirror/gm0. And as a last step before reboot you need add automatic geom_mirror.ko module loading:

echo geom_mirror_load=YES >> /boot/loader.conf

Double-check all, and reboot server. After reboot you need attach second drive to array:

gmirror insert gm0 /dev/ad6

If you check messages log now, you will find something like this:

GEOM_MIRROR: Device gm0: provider ad6 detected.
GEOM_MIRROR: Device gm0: rebuilding provider ad6.

Rebuild can take up to 6 hours, depends on HDD size, or system load. You can check rebuild process using this command:

gmirror status

Or more detailed output:

gmirror list

Also a good idea to add RAID status to monitoring.

When sync completed, you will have redundant system and ~2x faster IO (only read) performance.

This entry was posted on Thursday, December 21st, 2006 at 6:27 pm and is filed under Operation Systems, FreeBSD, How-To. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.