I see the man page has been expanded into steps already. I added what I think are helpful amplifications. What do you think? See the original man page reader complaint below. diff -u -r1.3 pvmove.8.in --- pvmove.8.in 4 Aug 2009 08:09:52 -0000 1.3 +++ pvmove.8.in 18 Jan 2011 18:30:16 -0000 @@ -40,14 +40,18 @@ details of all the data movements required. 2. 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. +for PEs that need moving according to the command line arguments. These PEs +are divided into "segments", runs of physically contiguous data where the PEs +are adjacent on a PV. For each such run 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. +from the original location to a newly-allocated location. A temporary +mirror is marked as such in the on disk metadata so that system knows now to +finish or undo the pvmove in the event it is interrupted by a system crash. The original LV is updated to use the new temporary mirror segment -in the pvmove LV instead of accessing the data directly. +in the pvmove LV instead of accessing the data directly, so that any writes +to the original LV are written to both segments until the temporary mirror +is syncronized. 3. The volume group metadata is updated on disk. @@ -58,7 +62,8 @@ 5. 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. +and writes a checkpoint into the volume group metadata on disk, so that +the step isn't repeated in the event of a system crash. Then it activates the mirror for the next segment of the pvmove LV. 6. When there are no more segments left to be mirrored, On 11/18/2010 05:06 PM, Stirling Westrup wrote: > On Thu, Nov 18, 2010 at 4:32 PM, Alasdair G Kergon <agk@redhat.com> wrote: >> 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. > The interpretation you give is only possible if one knows what the > man-page writer means by 'contiguous data', 'segment' and 'temporary > mirror'. As it was, I didn't and spent some time perusing the man > pages to find anywhere where these terms are defined, with no luck. > > So, yes, the man page definitely needs fixing. And that, perhaps, > should be done by someone who has a heck of a lot more familiarity > with the system than I have, or else the resulting man page is likely > to end up BOTH inadequate and erroneous. > > Still, I submit that if the man page needs to talk about checkpoints > AT ALL, then there needs to be a user method for determining, the > status of checkpoints during a pvmove. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
