Re: [lvm] [christophe.varoqui@free.fr: dm multipath target]

[James Bottomley <James.Bottomley@SteelEye.com>]

On Tue, 2003-08-19 at 04:51, Heinz J . Mauelshagen wrote:
> On Tue, Aug 19, 2003 at 11:04:31AM +0200, christophe.varoqui@free.fr wrote:
> No, device-mapper is designed completely generic (LVM2 as well BTW).
> It will never contain any vendor specific hacks.

We don't need it to contain any vendor code, but we do need an interface
for vendor specific additions.

How arrays accomplish a path switch is highly vendor specific.  Some
(like EMC) run all paths active, so nothing needs doing.  Others need a
specific command sent to the array down the path before the switch can
be done.

> Ghosts should report EIO in case of an unstarted LUN anyway ?
> In case they are started they are supposed to report EPERM on IO because
> they don't support any.

This is awfully vendor specific again.  I know, for example, the HP MSA
array will report a check condition, not ready.  I think we translate
this to I/O error in the mid-layer (best we can do).  This is why we'll
do a better job of error reporting in fastfail.

James