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Re: [dm-devel] dm howto?

thanks for getting back to me on this. note additional questions in the text.

On Jun 13, 2004, at 5:13 AM, christophe varoqui wrote:

Le dim 13/06/2004 à 05:15, gfbarros ualr edu a écrit :
is there documentation somewhere on making dm work with multipath in rhel3? im just wondering if most of this is already in the kernel provided by redhat before i start tearing things apart and rebuilding :)

I guess RedHat packages LVM1
and in no way it packages dm-multipath.
They plan to do so for RHEL4.
They are still lagging to integrate this in Fedora Core, so I'm not that
confident. Alastair should know better.

Right now, it's securepath for RHEL or nothing. DM will void your
support agreement.

for right now ill probably use mdadm for the boxes we _need_ to be supported, and ill start playing with dm on my debian ones. Just as a side, is there a dm patch for 2.4.x that i could try?

ive played with using mdadm a bit but it doesnt seems to deal with noticing dead paths and re-adding them too well...

Ive also noticed that disks presented by one of my controllers (hsv100) are not ready:

SCSI device sdb: 2097152 512-byte hdwr sectors (1074 MB)
sdb: asking for cache data failed
sdb: assuming drive cache: write through
 sdb:<6>Device sdb not ready.
end_request: I/O error, dev sdb, sector 0
Buffer I/O error on device sdb, logical block 0
Device sdb not ready.
end_request: I/O error, dev sdb, sector 0
Buffer I/O error on device sdb, logical block 0
 unable to read partition table

Yes, these are the ghosts paths :
each LUN is assigned to a single controler, so valid paths are all
through this LUN-master-controler. The other controler present ghost
paths, so that activating them doesn't need action on the host's side
(scsi rescan not needed).

is unloading/loading the module really the only way to rescan the bus with the qlogic hbas? i hate having to take an outage to add a vdisk.

but i only see this in my Debian box, the RHEL3 one only actually sees one path per controller pair... which im guessing is the one to the active controller. Im guessing that bad things would happen if that controller died, as the kernel would need me to reload the qla2300 module before seeing the new presentation... im assuming report_lun fixes this, how do i set that in the stock kernel? or am i sol?

Yes, Debian and standard kernel have to right behaviour.
Not sure what cause to different one in the RedHat kernel ... may be the
Qlogic failover implementation.

could the RH kernel be built without REPORT_LUN? would that do it?

whats your take on using the RH, HP, or qlogic versions of the hba driver? is one better than the others? how does the failover work? is there a doc somewhere with the module params?

would this have something to do with the HSV's not being really active-active? how is this dealt with? (is this the group_by_tur feature in multipath-tools?)

Some call this controler family "assymetric". IBM have the same case
with FastT ctlrs. Yes, group_by_tur was created for assymetric ctlrs.
The multipath policy works best with symmetric ones.

ill remember that next time we order equipment... :)

if this is not the right list for these questions, please steer me in the right direction :)

This is the one.


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Guil Barros - UALR Computing Services - Networks Project Manager
gfbarros ualr edu - http://www.ualr.edu - 501-569-3345
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