bdev manipulation at block layer level

bdev manipulation at block layer level

[Satish Kumar]

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 ?

Thanks !

regards,
Satish.






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Re: bdev manipulation at block layer level

[Jens Axboe]

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