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Re: LVM2 or MD mirroring?



On Fri, 2007-02-02 at 14:58 -0500, Brian Long wrote:
> I'm trying to decide on a methodology to use with a JBOD and software
> mirroring for RHEL 4 U4.  I understand I can try the new "lvcreate -m1"
> to create a mirrored LV, but LVM will choose the mirror for me and it
> won't allow snapshots of the LV.
> 
> Considering LVM mirroring is fairly new, do you think I should just
> mirror things with md and run pvcreate on the md devices?

Our experience in testing LVM mirroring with Apple Xserve RAID hardware
was that it is simply not ready for prime time.  Some of the issues have
been addressed in recent updates, and others can be fixed with command
line options, however, some things are simply too annoying.  For
example, a failure of a mirror device can lead to exceptionally long
delays in attempting to issue LVM commands (this is documented in Redhat
KB 8735).

We opted to use good old-fashioned md mirroring with LVM on top of the
md device.  This has proven to be quite robust, and doesn't limit us
from any of LVM's features.  Plus, I find it much easier to monitor the
status of the mirrors with /proc/mdstat than with anything that LVM
mirroring provides, but that might be my own brain damage (I've been
doing md mirroring for a long time with great success).

Later,
Tom



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