[linux-lvm] read only filesystem on LVM device after changing path in SAN

[Sebastian Reitenbach]

On Monday 08 June 2009 05:48:01 pm Sebastian Reitenbach wrote:
> Hi,
>
> I hope I am right here, if not, please let me know where would be a better
> place to ask. I have observed a problem on LVM based partitions when I
> change the paths through the SAN.
>
> Here my setup: I have a 3TB partition, coming from a SAN IBM DS4700, the
> same but smaller, for the operating system partition. Both presented to a
> xen host. On the data partition I have a LVM configured. There are four
> paths through the SAN for each of the disks. The host type on the DS4700
> for the server is configured as LNXCLVMWARE, which as for the documentation
> should be the right one.
>
> # multipath -ll
> Pilot-Project-VMs (3600a0b800048b31000000ffd4a10fd7e) dm-1 IBM,1814     
> FAStT [size=280G][features=1 queue_if_no_path][hwhandler=1 rdac][rw]
> \_ round-robin 0 [prio=2][enabled]
>  \_ 4:0:1:0 sdf 8:80  [active][ghost]
>  \_ 3:0:1:0 sdg 8:96  [active][ghost]
> \_ round-robin 0 [prio=12][active]
>  \_ 3:0:0:0 sdb 8:16  [active][ready]
>  \_ 4:0:0:0 sdc 8:32  [active][ready]
> Pilot-Project-Data (3600a0b800048b31000000fbe49f962e5) dm-3 IBM,1814
> FAStT
> [size=3.0T][features=1 queue_if_no_path][hwhandler=1 rdac][rw]
> \_ round-robin 0 [prio=2][enabled]
>  \_ 4:0:1:1 sdh 8:112 [active][ghost]
>  \_ 3:0:1:1 sdi 8:128 [active][ghost]
> \_ round-robin 0 [prio=12][enabled]
>  \_ 3:0:0:1 sdd 8:48  [active][ready]
>  \_ 4:0:0:1 sde 8:64  [active][ready]
>
> When I run a dd copy job, creating a file on the Operating system
> partition, e.g. dd if=7dev/zero of=/data/file then everything seems to be
> fine. I change the path through the SAN via the DS4700 management GUI, and
> the dd job keeps running as expected, so no problem without LVM.
> When I do the same on the LVM partition, then after some seconds, after I
> switch the preferred path through the SAN, then the LVM partiton becomes
> read-only, and the dd job dies. Then on the dom0, a
> fdisk -l /dev/mapper/3TB-Partion still shows output, but
> fdisk -l /dev/mapper/3TB--Partion-1 on the LVM device, just shows nothing.
> When I then shutdown the xen host, and do a:
> /etc/init.d/boot.lvm restart
> then fdisk -l /dev/mapper/3TB--Partion-1 on the LVM device, produces output
> again. However, the startup of the xen domU may still spit out errors, and
> the mounting of the device in the domU may still not work. I had to reboot
> the dom0 physical host to get the partition back in a working state.
>
> I do not have any kind of special configuration for the LVM device, I
> created it via yast2.
>
> Is there anything what I can do to prevent the LVM based partition to
> become read-only when a path in the SAN switches?
> If I need to provide more information let me know whats needed.
I guess I forgot the most important stuff:
kernel version: 2.6.27.21-0.1-xen x86_64
qla2xxx version:        8.02.01.03.11.0-k9
lvm2-2.02.39-17.6.2
multipath-tools-0.4.8-40.4.1
/etc/multipath.conf 

defaults {
        udev_dir        /dev
        path_grouping_policy    multibus
        getuid_callout  "--page=0x83 --whitelisted --device=/dev/%n"
        prio    "alua"
        user_friendly_names yes
        path_checker "rdac"

        default_features        "0"
}


>
> kind regards
> Sebastian
>