[DRBD-user] One large partition for external meta-data?

Arnold Krille arnold at arnoldarts.de
Tue Feb 19 22:35:52 CET 2013

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On Tue, 19 Feb 2013 07:19:04 -0800 (PST) isy
<isy at ipa.ruhr-uni-bochum.de> wrote:
> Having a LVM setup with about 50 partition already in use I've tried
> to setup drbd with external meta-data.
> 
> I created a new logical volume /dev/vg0/lvdrbd with 20G (I think it's
> more then enough!?):
> 
>   --- Logical volume ---
>   LV Name                /dev/vg0/lvdrbd
>   VG Name                vg0
>   LV UUID                ERwJml-5DQT-B11M-dd1E-nMgx-Fh5r-vmTrPu
>   LV Write Access        read/write
>   LV Status              available
>   # open                 12
>   LV Size                20.00 GiB
>   Current LE             5120
>   Segments               1
>   Allocation             inherit
>   Read ahead sectors     auto
>   - currently set to     1024
>   Block device           253:57
> 
> 
> Whenever I've got the time, I add a partition to the running
> drbd-config:
> 
> resource lv28 {
>   device minor 28;
>   disk /dev/vg0/lv28;
>   meta-disk /dev/vg0/lvdrbd[28];
>   on keller {
>     address 192.168.6.3:7728;
>   }
>   on schrank {
>     address 192.168.6.4:7728;
>   }
> }
> 
> so that all external meta-data of all partitions will be
> on /dev/vg0/lvdrbd
> 
> man drbd.conf:
> "You can use a single block device to store meta-data of multiple DRBD
> devices. E.g. use meta-disk /dev/sde6[0]; and meta-disk /dev/sde6[1];
> for two different resources. In this case the meta-disk would need to
> be at least 256 MB in size."
> 
> 
> When I submit
> 
> drbdadm create-md lv28
> 
> 
> the output SOMETIMES is like
> 
> md_offset 4026531840
> al_offset 4026535936
> bm_offset 4026568704
> 
> Found some data
> 
>  ==> This might destroy existing data! <==
> 
> Do you want to proceed?
> [need to type 'yes' to confirm] yes
> 
> Writing meta data...
> initializing activity log
> NOT initialized bitmap
> New drbd meta data block successfully created.
> success
> 
> 
> It is SOMETIMES, not always, but I'm getting nervous about it...
> 
> Can anyone tell me, what I'm doing wrong??

I am using external meta-data myself. And on one of the servers I get
similar output when creating the md, on the other there is nothing. The
difference is that on one machine its pristine hard-disk-space that
wasn't written to before, on the other machine (the one where it
detects "data") was written to before (some destructive write-tests for
performance tests).

So I think (hope?) all is well for us.

You could have filled that meta-data partition with zeros before. But
once its used for one some meta-data, its to late for that...

Have fun,

Arnold
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