I'm not a Linux LVM specialist, and I think your problem is not very much 
to iSCSI. However I think you problem was to use "pvcreate --uuid 
<UnknownDeviceID>" on a new disk. UUID means "universally unique ID". So if 
"new" disk has the same UUID as the old disk, the OS is allowed to assume that 
new disk actually is the old disk. So probably the LVM would only re-sync the 
stale extents of the PV, while the data in the buffer cache is still valid (I 
assume that disconnecting a SCSI disk from the bus (that is what you did) does 
invalidate the OS block/buffer cache.

I may be wrong however.


On 4 Dec 2008 at 5:25, HIMANSHU wrote:

> Hi all,
> This is the surprising scenario.
> I created a VG containing one local and one remote(iSCSI) disk taken
> from target.Then I created 2-3 LV's  with file system on it and filled
> them all with some data till they become full.Then I removed remote
> disk i.e. perform logout operation of iSCSI disk.
> So this VG became inconsistent.I can see that using "pvscan" where I
> will see "unknown" device in front of this VG Name.
> Then I replaced the remote disk with any other disk using "pvcreate"
> as follows.
> pvcreate --uuid "<UnknownDeviceID>" --restorefile /etc/lvm/backup/
> <VGNAME> <New disk>
> and to my surprize,I found that I got all my data which is even on the
> remote disk.How is this possible?
> I am not having any RAID configurations here.I am having whole disk as
> a PV,not the partitions and LV's on that Physical volumes are created
> in a way that they are having their major parts on remote disk(In my
> case,2GB data was there on remote disk).
> How full data is derived from the metadata here?
> > 

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