[DRBD-user] Re: drbd-user Digest, Vol 11, Issue 23

Maurice Volaski mvolaski at aecom.yu.edu
Sat Jun 25 18:46:25 CEST 2005

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

>/ 2005-06-25 03:44:03 -0400
>\ Maurice Volaski:
>>  >But now I have to shrink one. That's more complicated. The question
>>  >is whether drbd resize will know to use the filesystem's size, which
>>  >is correct, or the lvm size, which, since it hasn't been reduced yet,
>>  >is wrong? If it picks the wrong one, should I give it the
>>  >filesystem's exact size (fdisk -s device)?
>>  The way I did it was to create the logical volume, drbd device and
>>  filesystem in the correct size on the second system with it being
>>  unconnected. I used fdisk -s to find out filesystem's corrected
>>  (shrunken) size (in K). That means that the size parameter to pass to
>>  drbdsetup's resize is that size + exactly 128 MB (in K).
>fdisk -s gives you the size of the partition,
>not the "filesystems's exact size",
>so it will give you the size of drbd,
>no hint of where to shrink to.
>but you typically tell the "resize filesystem" operation,
>to which size you want to resize to. then, that should be the size.

The wrong logical volume was 375 GB. My goal was to make it 370 GB, 
to shrink it by 5 GB.
fdisk -s on this one was 393084928K. That's 374.875 GB, which is 
exactly 128 MB smaller than the logical volume. I'm assuming drbd 
metadata sits in that space.

On the right one, logical volume is 370 GB and fdisk -s reported 
387842048K, which is 369.875 GB, which is also exactly 128 MB smaller 
than the logical volume.

So for the wrong one above, I passed 387842048K to resize2fs and the 
value 387973120K, which is really the size of the logical volume, 370 
GB, to drbdsetup resize. And finally passed 370G to lvreduce.

Are you saying my math doesn't add up?

>btw, you do NOT want to resize a drbd with internal meta data.
>use external meta data (that is easy on lvm).
This is scary. Why? Is this in the docs anywhere or even on the 
mailing list? What bad will come of it? (So far, it is syncing like 
the others, no errors...yet).

Anyway, it seems I should be creating a separate logical volume just 
to store all the metadata? If I do that now, will drbd know to 
relocate the existing meta-data or will I have to start fresh and 
sync everything from scratch?

Maurice Volaski, mvolaski at aecom.yu.edu
Computing Support, Rose F. Kennedy Center
Albert Einstein College of Medicine of Yeshiva University

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