Hi Dmitry,
I'm using a setup very similar to yours apart from the last part - I use
a 1 LV to Xen partition mapping for all of our PV domUs. Its only the
HVM ones which I use as a full disk image, but anyway its not too relevant.
Our backup strategy currently involves taking daily LVM snapshots and
rsyncing data from them (or backing up using dd in case of HVM). Doing
this means you aren't doing anything to the underlying device so removes
any risk - just make sure your snapshot is big enough to cope with the
amount of data that will change whilst it exists.
Whenever I do a resize of a LV & subsequent DRBD device I always
schedule a reboot of the domU afterwards to make sure that the OS
properly picks up the resize. I've not had any problems with either of
these approaches so far.
On 21/07/09 22:49, Dmitry S. Makovey wrote:
Hi everybody,
we're running LVM-DRBD-Xen-LVM sandwich on our boxes and got an interesting
question:
as you can see from above we have LV (say /dev/system/lv1) which we use as a
base for DRBD device (say /dev/drbd0, named "vmspace") which is then used as
a raw disk for Xen VM (say myVM). Inside of myVM we use LVM again to manage
partitions etc. (say we have /dev/vmsystem VG inside with lots of various LVs
in that VG).
Now above we've used to be able to dynamically grow our VMs if needed.
Scenario looks like this: we do
lvresize /dev/system/lv1
drbdadm resize vmspace
...inside of VM
fdisk /dev/xvda
...add another partition /dev/xvda3
vgextend /dev/xvda3
lvresize /dev/vmsystem/lvX
resize2fs /dev/vmsystem/lvX
Now another thing that happened after using above scenario:
running fdisk -l /dev/system/lv1 we saw different picture on primary and
secondary DRBD box until secondary was rebooted.
Now the actual questions:
1. why did fdisk report /dev/system/lv1 layout different for primary and
secondary (probably not-so-much DRBD question, but it kind of is related). By
different I mean - it was showing the size of /dev/xvda correctly, but it was
showing only 2 partitions on secondary box and 3 on primary
2. is it OK to use LVM snapshots for /dev/system/lv1 on secondary box to
create "copies" of running VM to get some migration/testing done? (I realize
problems about snapshoting running system, but are there any other problems)?
3. I remember seeing some information about "not touching raw devices
underneath DRBD devices" and I also remember reading that even read-only
mounts along with other apparently "innocent" operations still modify
underlying devices. Does anybody have reference to the list of those "big
no-no's" ?
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