Some GMirror questions.
clarkp at mtmary.edu
Fri Jun 4 17:39:41 UTC 2010
There are a number of gmirror resources available online but there are a
few discrepancies. I thought someone here might be able to shed some
light on them. Also, this is on FreeBSD 8.0 RELEASE.
Does creating the mirror need to be done from a Livefs CD (in Fixit
mode) or can it be done directly from the OS? The Handbook makes no
reference to things like:
# Install FreeBSD on to ad0.
# Reboot with the Install CD.
# Enter Fixit mode.
mount -t devfs devfs /dev
gmirror label -v -b round-robin gm0 /dev/ad0
mount /dev/mirror/gm0s1a /mnt
echo geom_mirror_load="YES" >> /mnt/boot/loader.conf
It just indicates jumping right in with gmirror label from the OS (at
least it seems to).
Also, these next 2 entries in /etc/rc.conf. The Handbook does not make
any mention of them. The way the authors state their purpose it would
seem as though that should be done in all cases of disk mirroring. Is
# tell the system that the swap file will be on a mirror, not a raw drive.
echo ’swapoff=”YES”‘ >> /mnt/etc/rc.conf
# need to do this to make dumping cores happy since it won’t use a
Lastly, I know at one point the 'load' algorithm had some performance
problems and people were saying to only use 'round-robin'. It seems as
though some code was committed back in Dec 2009 to fix it's this. Is
there a practical rule of thumb to using 'load' vs 'round-robin'? Is
this an accurate way to look at it?
"Round-robin because if you have two disks in a mirror, they’re both
under the same 'load' constraints, and it is best to KISS."
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