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LVM issue.

Frequent Advisor

LVM issue.

Hi All,

I have old lvs which have Consistency Recovery as NOMWC. I have created a new vg and lvols in that vgs. However i am unable to set the Consistency Recovery as NOMWC . It is showing as MWC. This is a 2 node cluster.

Should i use vgchange or lvchange.
I did this:
Turn the mirror write cache off on a logical volume:

lvchange -M n /dev/vg01/lvol1

Can some one help me on this with complete syntax.

Also, please explain MWC NOMWC NONE options.

R.K. #
Honored Contributor

Re: LVM issue.

Hello Ravi,

Here is what you can follow:

View the current consistency recovery policy
# lvdisplay /dev/vg01/data
Consistency Recovery MWC
Disable the MWC
# umount /data
# lvchange â M n â c y /dev/vg01/data
# mount /data
Verify that the change succeeded
# lvdisplay /dev/vg01/data
Consistency Recovery NOMWC

*The MWC policy introduces some runtime overhead, but guarantees fast consistency
recovery after a system crash, even for very large logical volumes. The MWC policy is
appropriate for most data logical volumes, especially for very large logical volumes that
would take a long time to resynchronize after a crash without the MWC/MCR.
â ¢ The NOMWC policy requires no runtime overhead, but may take longer to recover mirror
consistency after a system crash. The NOMWC policy is appropriate when runtime
performance is critical, and recovery time is less of concern.

If you choose to use the NOMWC policy, and a system crash occurs, LVM will spawn
nomwcsyncd daemons at activation time to resynchronize each mirrored logical volume that
was open at the time of the crash.

nomwcsyncd doesnâ t just synchronize portions of the logical volume that had pending writes
at the time of the crash; it synchronizes the entire logical volume from top to bottom. For
large logical volumes this may take a long time. Fortunately, the daemon runs in the
background so system activity may proceed while LVM does the synchronization.

â ¢ The NONE policy requires no runtime overhead, but leaves your mirrors in an
inconsistent state after a system crash. This policy is often used for swap logical

Extracts taken from LVM student's guide.

Hope this helps !
Don't fix what ain't broke