[dm-devel] [patch] mpath_prio_pp
T S, Veena (STSD)
veena-s.t at hp.com
Thu Jan 17 10:44:49 UTC 2008
> -----Original Message-----
> From: Kiyoshi Ueda [mailto:k-ueda at ct.jp.nec.com]
> Sent: Friday, January 11, 2008 4:18 AM
> To: T S, Veena (STSD)
> Cc: dm-devel at redhat.com
> Subject: Re: [dm-devel] [patch] mpath_prio_pp
>
> Hi Veena,
>
> On Wed, 9 Jan 2008 15:15:38 +0530, "T S, Veena (STSD)" wrote:
> > Purpose of the patch-
> > -- To introduce the prio_callout attribute into the
> multipath section
> > of the configuration file.
>
> The prio_callout feature has been changed to the libprio.
> Please check the latest Christophe's git.
>
The changes made, to have the prio_callout attribute in the multipath
section
can be ported to the latest Christophe's git.
>
> > -- To implement the preferred path feature in device mapper.
> >
> > Uses of the patch-
> > -- Prio_callout attribute in the multipath section allows users to
> > write callout routines,which can be specific to a LUN.
> > -- When it is known the performance of one of the path is
> better than
> > the other available paths for a particular LUN, the user
> can set it as
> > preferred path.
>
> How about opposite case such as the performance of some paths
> are better than the one backup path for a particular LUN?
> So if we can specify some preferred paths, that may be more useful.
>
The preferred path approach implemented here is only an example to show
how
the selection of path(s) can be made for a particular LUN. Changes to
have
more than one preferred path can be made accordingly,if necessary.
>
> > +int main(int argc, char * argv[])
> > +{
> > +
> > + char path[FILE_NAME_SIZE];
> > +
> > + if(argv[1] && argv[2])
> > + {
> > + if(!strncmp(argv[2],"/dev/",5))
> > + strcpy(path,argv[2]+5);
> > +
> > + if(!strcmp(path,argv[1]) ||
> !strcmp(argv[1],argv[2]))
> > + {
> > + printf("%u\n", HIGH);
> > + return 0;
> > + }
> > + else
> > + {
> > + printf("%u\n", LOW);
> > + return 0;
> > + }
> > + }
> > + return -1;
> > +}
>
> This prioritizer looks that we need to specify the preferred
> path by devnode or major/minor, right?
> If so, it doesn't work reliably.
> Both devnode and major/minor may vary for each system reboot.
> It's horrible to check and change the config file after every reboot.
> We should be able to use more persistent name to specify a
> path, though I don't have a good idea now...
>
> Thanks,
> Kiyoshi Ueda
>
Thanks,
Veena
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