Re: RAID readonly before final shutdown

On Wednesday August 10, gbakos@cfa.harvard.edu wrote:

Hi,

The entire OS I am using is running on software RAID-1. Before killing
the power of the UPS (in case of a power outage), I issue:

/sbin/mdadm --readonly $RAIDDEV
on all the RAID devices I have.

This, however, does not seem to be enough, and when i power the system
back on, the RAID arrays are not clean, and a long syncing starts. A
last step is missing; something like marking the arrays that they are
clean. I see this happening for a flash of a second when i tell the PC
to "/sbin/poweroff", i.e. "halt -p". The very last second, before the
ATX power is turned OFF, the kernel does something to the md arrays.

My questions are:
1. What exactly is this last step?

It is exactly switching the arrays to readonly.

2. Can I achieve it manually by sth like
 echo *** > /proc/***

no (maybe echo ?? > /sys/block/.... one day).

or by using mdadm?

no.  You can only switch an array to read-only when it is not in use.
So you have to unmount it first.  That possibly sounds a bit
pointless, and it probably is.  But it hasn't been a high priority.

If you are using 2.6, then the arrays will be automatically marked
clean after 20ms of inactivity.  If you "kill -9" the "md*_raid1"
processes, then it will start marking the array clean the instant of
inactivity.

NeilBrown