Re: bdev manipulation at block layer level

From: Jens Axboe (
Date: Wed Jul 25 2001 - 04:50:55 EST

On Wed, Jul 25 2001, Satish Kumar wrote:
> Hi,
> I have a host PC connected to a disk array with
> alternate paths to an end scsi disk.
> I attempted load balancing across paths by changing
> the b_dev & b_rdev ib the bufer_head list in
> ll_rw_block function of ll_rw_blk.c (block layer), and
> was successful in load balancing with data integrity,
> on linux 2.2.16.
> However, when I try the same stunt with a linux 2.4 (
> &2.4.2) kernel, I am seeing corruption occasionally.
> Can anyone let me know if I am missing anything ?

You must not change b_dev, that will screw the cache! Just change b_rdev
to redirect the I/O and it should work.

Jens Axboe

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