Re: [patch] raid1: allow user to force reads from a specific disk

From: Chuck Ebbert
Date: Mon Aug 07 2006 - 04:47:44 EST

In-Reply-To: <17622.35724.43741.529875@xxxxxxxxxxxxxxx>

On Mon, 7 Aug 2006 10:38:36 +1000, Neil Brown wrote:

> > Allow user to force raid1 to read all data from a given disk.
> > This lets users do integrity checking by comparing results
> > from reading different disks. If at any time the system finds
> > it cannot read from the given disk it resets the disk number
> > to -1, the default, which means to balance reads.
> Could say a little bit more about why you want this?
> You could get nearly the same situation be setting the other drives to
> write-mostly.

But you couldn't test whether all IO had really gone to the target disk
after doing some reads.


echo 0 >/sys/block/md0/md/read_from_disk
mount -t ext3 /dev/md0 /mnt/md0
find /mnt/md0 -type f | xargs md5sum
cat /sys/block/md0/md/read_from_disk

If the output from the last command isn't 0 then not all reads came from
that disk.

> And the more thorough integrity check is available via
> echo check > /sys/block/mdX/md/sync_action

I tried that. It doesn't do anything but print the raid status to the
kernel log. Either that or on my 100MB mirror it's able to thoroughly
check the integrity in less than 1/4 second.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at