[Beowulf] RAID5 rebuild, remount with write without reboot?

[mathog]

On 05-Sep-2017 12:00, Joe Landman wrote:

> On 09/05/2017 01:28 PM, mathog wrote:
>> Short form:
>> 
>> Is there a method to remount the logical volumes writable
>> that does not require a reboot?
> 
> Generally the FW would write lock it.  A
> 
>      mount -o remount,rw $path
> 
> may not clear this.  I've found that I need to often do something akin 
> to
> 
>      echo "- - -" > /sys/class/scsi_host/host0/scan
> 
> for each scsi host bus.  Another thing to try is to remove the driver
> and modprobe it again.  However, as your /boot and / are on it, this
> probably won't work well.

/boot wasn't, only / was.

Is there a difference between "mount -o remount" and "mount -a" if the
partions/logical volumes are already mounted "ro"?   The system could 
read
/etc/fstab which indicated that the mount should be rw.  It isn't clear 
to me from the man page what mount is supposed to do in that case.

Also, can anybody suggest what could possibly differ between

   RAID degraded=1, logical volumes mounted ro, 1 disk failed, 1 disk 
offline

and

   RAID degraded=1, logical volumes mounted ro, RAID 1 disk failed, all 
others online

such that "cat" and "more" did not work in the former but did work in 
the latter, while "ls" and "megacli" worked in both?

At this point I have that just "happy to be walking away" feeling about 
the whole incident.

Thanks,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech