[Pkg-iscsi-maintainers] Bug#498616: Unmounting LVM'd isci based filesystem

[Ritesh Raj Sarraf]

Hi,

I think there are 2 parts to this problem.

1) iSCSI + Multipath + LVM

I am not sure how is it handle during start-up. Suppose you have 256 LUNs with 
4 path each. This would result in a large 1000+ scsi device list. Discovering 
these many devices will take some time. And on that, dm-multipath will also 
take time in identifying these devices.

I think to tackle iSCSI + Multipath + LVM, during start-up, we will need a 
custom udev rule to identify Multipathed iSCSI PVs.


2) As one, but during shutdown.
Okay!! Here I think we might be in a trickier situation. To be able to unmount 
iSCSI + Multipath + LVM devices we need a 3 step process.

a. Offline the VG
b. Delete the maps
c. Then stop iSCSI


Currently, in iSCSI this is not handled. And I think if you have a setup like 
this for LUNs referenced in fstab through they LV names, iSCSI might just 
ignore them and shutdown the service. Thus this will lead to a hang state.

To handle this scenario, I think we need a way to tear down the logical 
devices and identify their physical scsi devices. Once we have the scsi device 
names, umountiscsi.sh can determine if it is an iSCSI device or not. And if 
so, it will not stop the iSCSI service (Part of this change has been put into 
2.0.871.3-1, pending to be uploaded to Sid)


Regards,
Ritesh


On Monday 19 Jan 2009 04:30:29 Javier Barroso wrote:
> We (as debian user) have another problem with lenny and iscsi + lvm +
> multipath (should I open another bug?). I try to explain it here:
> 
> # pwd
> /etc/rc6.d
> # ls -1 *multipath* *iscsi* *lvm*
> K20multipath-tools
> K80umountiscsi.sh
> K81open-iscsi
> S50lvm
> S50lvm2
> 
> Suppose I have a pv in iscsi lun, and over it a vg, who has a lv.
> So if multipath is down, how umountiscsi is capable to unmount lvm volume?
> 
> My server hangs forever when is rebooting or shutting down. With sys+rq W
> debian said to me there is a process lvchange who is blocked. I can read
> in redhat issue tracker [1] about similar bug in redhat systems.
> 
> Is it possible to "full" support lvm inside iscsi luns ?
> 
> Any help is apreciatte.
> 
> Thank you.
> 
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=212265
> 
> Debian Rocks!

-- 
Ritesh Raj Sarraf
RESEARCHUT - http://www.researchut.com
"Necessity is the mother of invention."
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