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

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;
}

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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