[Xen-users] LVM partition resize pain...

[Erich Weiler <weiler@xxxxxxxxxxxx>]

Hi All-

Was hoping someone would know what's going on here....

I created a Xen VM on top of a LVM volume.  The volume was like 530GB 
big.  Within the volume sits the VM, with 5 partitions, one of them 
500GB big (the other 4 file systems comprise the other 30GB).  Each 
virtual disk partition exists as /dev/xvda1 - /dev/xvda5.  /dev/xvda5 is 
the one with the 500GB file system on it.
I wanted to reduce the size of the filesystem on /dev/xvda5 from 500GB 
to 5GB.  So I unmount /dev/xvda5 then run:
# resize2fs /dev/xvda5 5G

Works great.  Next, I shut down the VM and reduce the size of my logical 
volume:
# lvreduce -v -L 40G /dev/vg0/xen1

So the volume is still larger than all the filesystems in it, such that 
I don't lose any data.  The command worked successfully.  Then I booted 
the VM and got errors on boot say something about "/dev/xvda: wanted 
500000000 but was limited to 5000000" or something like that.  But the 
VM booted even after the errors and appeared to work OK.  So I:
# fdisk -l

Disk /dev/xvda: 32.2 GB, 32212254720 bytes
255 heads, 63 sectors/track, 3916 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1   *           1          13      104391   83  Linux
/dev/xvda2              14        1288    10241437+  83  Linux
/dev/xvda3            1289        2308     8193150   82  Linux swap / 
Solaris
/dev/xvda4            2309       67620   524618640    5  Extended
/dev/xvda5            2309       67620   524618608+  83  Linux

Notice it says that /dev/xvda is 32.2GB (which is correct), but 
/dev/xvda4-5 still think they are 500GB big!  A 'df' shows that the 
filesystem is really only 5GB though, as expected.  I tried some parted 
magic but parted can't do anything (even print the partition table!), I 
get errors like:
[root@template ~]# parted /dev/xvda
GNU Parted 1.8.1
Using /dev/xvda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Error: Can't have a partition outside the disk!
(parted)

and it won't let me make changes, etc.  Is there something I missed? 
Wasn't the OS supposed to recognize the size change in /dev/xvda on 
boot?  Or do I have to manually change the disk label or something?  Is 
it just impossible to resize a VM's file system then change the volume 
the VM sits on to reflect the change?
Thanks so much for any ideas!

-erich


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