What about write balancing ?

I would also be interested in discussing a possible patch to the raid code to 
do write/read balancing over N hba's if it is that trivial.

On April 8, 2002 03:16 pm, Luca Berra wrote:

On Mon, Apr 08, 2002 at 02:02:56PM -0500, SoulBlazer wrote:

quoted

Question,

I have 2 Qlogic Fiberchannel HBA's (2100F's) connected directly to both
FCAL ports on my Sun A5200 22 Disk disk array.  If I enable multipath, do
I get twice the throughput between my linux box and the array ? Or is
multipath purely for failover.

Additionally do I get twice the bandwidth anyhow since both HBA's see the
same disk ?  How can I tell if either one or the other or both hba's are
being utilized...

multipath does not do any read-balancing (see code below),
while i don't think it would be difficult to implement (cut&paste from
raid1.c) i did not have any time to try

only way i found to do read-balancing at the moment is if you have multiple
luns on your array you can create md configs with alternating channel
order.

regards,
Luca

------- from 2.4.18-rc1/drivers/md/multipath.c
static int multipath_read_balance (multipath_conf_t *conf)
{
        int disk;

        for (disk = 0; disk < conf->raid_disks; disk++)
                if (conf->multipaths[disk].operational)
                        return disk;
        BUG();
        return 0;
}