[DRBD-user] failure on offline shrinking

Lars Ellenberg lars.ellenberg at linbit.com
Tue May 19 16:25:54 CEST 2009

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Tue, May 19, 2009 at 09:42:31AM -0400, Chad Phillips wrote:
> On May 18, 2009, at 12:01 PM, Stefan Seifert wrote:
> > On Thursday 14 May 2009 18:37:47 Chad Phillips wrote:
> >> running the latest CentOS release of drbd (8.2.6), and tried to  
> >> shrink
> >> a DRBD device backed by LVM.  here's an abbreviated running log of
> >> what i did with the error at the end:
> >
> > Just a question: why didn't you shrink the drbd device online? From  
> > the
> > description in the drbd user's guide that would seem much easier and  
> > thus
> > safer.
> from my searching, it didn't seem safe to shrink an ext3 filesystem  
> online, only to grow it.
> the alternate procedure i used looked like the only choice to me.
> however, re-reading the doc, it now seems like it wouldn't be  
> necessary to shrink the filesystem online in order to shrink the drbd  
> device online.
> would this procedure have worked instead?
> 1. leave drbd running in primary/secondary
> 2. umount the filesystem
> 3. resize the filesystem offline
> 4. drbdadm -- --size=new-size resize resource
> 5. lvreduce the partition
> 6. remount the filesystem

probably not for internal meta data :(
I think the meta data is not relocated until it is too late...

actually, your original approach should have worked just fine.
only you did not decrease the bitmap, so it tried to restore
the 8 MB worth of bitmap necessary for your previously 250 G backing
store, but should have only restored ~1.2 MB of bitmap for your now only
39 G bit backing store.  there are a lot of sanity checks in restore-md
missing, "user" is supposed to know what she is doing.

admitted, we should provide some cleaner, less error prone,
better way to handle resize of internal meta data.
but we don't, yet.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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