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Re: A quite tricky LVM issue



On 03/30/2010 02:30 PM, Hans de Goede wrote:
Hi All,

While doing what should be testing a simple iscsi related patch,
I encountered the following issue:

Take a system with a single disk, sda, which has a /boot on
sda1 and a PV on sda2. This PV is the PV for the 1 PV VG:
VolGroup, which contains LV's lv_swap, lv_root and lv_home.

"Attach" an iscsi disk to this system, which becomes sdb,
which has a /boot on sdb1 and a PV on sdb2. This PV is the PV
for the 1 PV VG: VolGroup, which contains LV's lv_swap and
lv_root.

Notice that:
1) The 2 VG's have the same name
2) Only sda has a lv_home LV.

Now in the filter UI select only disk sdb to install to, then
the following may (depending on scanning order) happen:

Assume sdb gets scanned first by devicetree.py:
- when scanning sdb2, handleUdevLVMPVFormat() will
call "lvm lvchange -ay" for all LV's in this VG
(as seen by udev, more on that later).
- at this point, sda has not been scanned yet, so
isIgnored has not been called for sda2 yet, and thus
lvm_cc_addFilterRejectRegexp("sda2") has not been called
yet.
- thus lvm lvchange sees both sda2 and sdb2, it complains
that there are 2 identically named VG's and picks the one
using the sda2 PV.

Maybe we should stop the installation at this point and tell the user that he named two VGs the same and needs to address this before proceeding with the installation? Because otherwise we will need to do too many changes for a corner case that only occurs infrequently. And we still won't be completely happy with them.

Ales


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