[linux-lvm] Move pvmove questions Was: Need help with a particular use-case for pvmove.
Alasdair G Kergon
agk at redhat.com
Thu Nov 18 21:32:58 UTC 2010
On Thu, Nov 18, 2010 at 03:40:25PM -0500, Stirling Westrup wrote:
> It mentions checkpointing, but gives no further information. It
> certainly doesn't say anything about how often they are done, or under
> what circumstances.
It's in there, but the man page would indeed benefit from more repetition
and examples. Patches welcome!
Every logical volume in the volume group is searched for *contiguous
data* that need moving according to the command line arguments. For
each piece of data found, a new *segment* is added to the end of the
pvmove LV. This segment takes the form of a *temporary mirror* to copy
the data from the original location to a newly-allocated location.
A daemon repeatedly checks progress at the specified time interval.
When it detects that the first *temporary mirror* is in-sync, it breaks
that mirror so that only the new location for that data gets used and
writes a *checkpoint* into the volume group metadata on disk.
So checkpoint at first daemon check interval after temp mirror in-sync, and
one temp mirror per item of contiguous data to be moved.
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