[DRBD-user] Shrinking Filesystem

[CA Lists]

> On Fri, Jun 22, 2007 at 09:24:09AM -0500, CA Lists wrote:
>> I have two iSCSI targets that I have drbd 8.0.3 running on (CentOS 5). I'm
>> using OCFS2 on my nodes. My question is, which filesystem do I need to
>> shrink for DRBD? Do I want to shrink the iSCSI disk on the nodes
>> (/dev/sdb1), the actual block device on both iSCSI targets (/dev/sdb), or
>> the drbd device on the iSCSI targets (/dev/drbd0)? And can I do this after I
>> have used OCFS2 to format the disk? Thanks,
> 
> 
> ===== situation without drbd: =====
> 
> |- ~/.../~ - /dev/some/storage -- ~/.../~ -----------------------------|
> 
> ===== situation with drbd, and external drbd metadata: =====
> 
> completely transparent wrt. /dev/some/storage,
> no need to change anything. you just have to have some other block
> device available for drbd meta data.
> 
> 
> |- ~/.../~ - /dev/drbd0        -- ~/.../~ -----------------------------|
> |- ~/.../~ - /dev/some/storage -- ~/.../~ -----------------------------|
> 
>                |- drbd-md: /dev/other/storage -|
> 
> 
> ===== situation with drbd, and internal drbd meta data: =====
>                
> |- ~/.../~ - /dev/drbd0        -- ~/.../~ -------|- drbd-md: INTERNAL -|
> |- ~/.../~ - /dev/some/storage -- ~/.../~ -----------------------------|
>                                                  |.....................|
>                                                   these are the last
>                                                   blocks of your
>                                                   /dev/some/storage
>                                                   so if you had
>                                                   any useful
>                                                   data here,
>                                                   make sure you move
>                                                   it away before you
>                                                   overwrite this area
>                                                   with drbd meta data
> 
> depending on what has been there (file system, partition, lv),
> there are different means to do so.

There was nothing on the drives at all. In a chicken-before-egg type of
situation, since I don't have /dev/sdb mounted anywhere on the iSCSI
targets, I thought I would need to get OCFS2 up and running on one of the
nodes and format the drive to be able to do anything with it. Then, I found
out ocfs2 provides no way to shrink a filesystem.

I found this and am trying to follow it:
http://www.gossamer-threads.com/lists/drbd/users/9161

I have no way to get the "Block count" and "Block size" via tune2fs since
it's ocfs2 not ext2/ext3. However, is the value from "df" useful at all?

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdb1            975699648   1224960 974474688   1% /data

Cat /proc/partitions | grep 'drbd0' shows
 147     0  975670156 drbd0

So, /proc/partitions shows a number that is 29492 smaller, which means bad
things, right? In other words, I need to probably re-make the ocfs2 file
system to be smaller, correct?

Thanks for the help.

> 
> 
> hth.
>