[Linux-cluster] Re: USB flash drive no longer mounted read/write under RHEL

[Robert Peterson]

sun sadm wrote:
> Hi colleague,
>
> please share your comments about this issue. We have a similar problem
> in cluster environment where SAN disks get read only (mtab and mount
> say rw). We absolutely don't know why this happen. How can we
> troubleshoot this?
>
> We opened a ticket at EMC (our SAN provider) and they claim its a RHEL 
> problem.
>
> Nico
Hi Nico,

Have you spoken to Red Hat Tech Support about this?  I doubt whether 
your problem
is related to the USB flash drive issue, although it's hard to rule it 
out without
more info.

Before we can help, we need to know more about your situation, such
as what file system you are using, what version of the Cluster Suite you 
are using,
and what messages appear in /var/log/messages from all nodes in the cluster.

If it's on a SAN in a cluster, I'm assuming it's GFS, in which case you 
can do some
things, like (1) checking for errors in /var/log/messages, (2) check 
/proc/mounts to see
if the kernel also thinks that it's mounted RW.  (3) make sure the 
cluster bit in
on for the volume group:  do the vgs command and check if it has a
"c" in the flags, e.g. "wz--nc" and not "wz--n-".

If the data on the drive is expendable and you can afford to lose it, 
you can
do some experiments writing data to the raw device.  For example,
unmount the file system from ALL nodes and do something like:

(save off some raw data from the lv)
dd if=/dev/your_vg/your_lv0 of=/tmp/test1 bs=1024 count=1
(write the saved data back to the lv)
dd if=/tmp/test1 of=/dev/your_vg/your_lv0 bs=1024 count=1

If that doesn't work, try writing to the SCSI device directly.
Assuming that /dev/sda is part of your vg on the SAN:

(save off some raw data from the SCSI device)
dd if=/dev/sda of=/tmp/test1 bs=1024 count=1
(write the saved data back to the raw device)
dd if=/tmp/test1 of=/dev/sda bs=1024 count=1

NOTE: These commands are dangerous and should not be attempted
on production machines with live data.

I think some fibre channel SANs can be configured to restrict access
to the data, so you may have to check that as well.  Just some ideas.

Regards,

Bob Peterson
Red Hat Cluster Suite