From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philip R Auld Subject: Re: [dm-devel] [multipath] SCSI device capacity mess Date: Wed, 27 Oct 2004 16:28:21 -0400 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20041027202821.GO2853@vienna.egenera.com> References: <1098833278.4914.24.camel@zezette> <20041027081713.GC32712@marowsky-bree.de> <1098903759.12464.32.camel@zezette> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from roadrunner-base.egenera.com ([63.160.166.46]:26786 "EHLO coyote.egenera.com") by vger.kernel.org with ESMTP id S262675AbUJ0U1z (ORCPT ); Wed, 27 Oct 2004 16:27:55 -0400 Content-Disposition: inline In-Reply-To: <1098903759.12464.32.camel@zezette> List-Id: linux-scsi@vger.kernel.org To: christophe varoqui Cc: device-mapper development , "linux-scsi@vger.kernel.org" Rumor has it that on Wed, Oct 27, 2004 at 09:02:39PM +0200 christophe varoqui said: > > > > Some SAN hardware present for a same LUN a bunch of valid paths and a > > > bunch ghost paths. In my case, the ghosts responds to standard INQUIRY > > > (EVPD 0x83, 0x80, ...) but the READ_CAPACITY fails : > > > > As a note, this is one mode the EMC CLARiiON arrays can also operate in. > > Even worse, they won't present the block device at all, just the SCSI > > generic mode. However, for the CLARiiONs, they can be configured to > > behave sanely and reply to a READ_CAPACITY too (just all I/O will be > > errored), if setting the failovermode to 1. > > > > I wonder whether your system can also be configured as such? > > > Yes it could, but it's a controler wide setting. > So is the CLARiiON setting. > Compatibility with other OS sharing the same controlers might impose > this mode though. So I'd like to straight this situation up. > I suspect anything else doing failover on this device would already require that setting. And if not doing failover probably won't see the passive controller due to cabling/zoning setup. I don't see anything wrong with asking for specific array settings if they are needed for multipathing. Some arrays don't return meaningful LU IDs if not configured for it. > > > > > > 1) make the /sys/block/*/size attribute writable > > > 2) resurrect a BLKSETSIZE ioctl > > > 3) make device-mapper less strict, and hope we can fix the size by a > > > device rescan when it get activated > > > 4) sell the culprit hardware > > > > Personally I would opt for 4), but 3) is the likely path to solve this. > > > > Using the new priority group initialization code (where we sent magic > > commands down to activate the newly switched-to PG) which Alasdair and I > > are currently doing for the CLARiiON pampering and which provides a > > plugin-architecture to the dm-mpath system, you should be able to plug > > in a hardware-specific handler for your system too. > > > > However, "relaxing" this check should likely also be a property of the > > hardware plugin loaded; I'd not wish to have it relaxed in all > > scenarios. > > > I wonder if it's not simpler just to remove the NOSTARTONADD flag on > this devices in scsi_devinfo.c. I tested that and all the READ CAPACITY > succeed as expected (DEC HSG80 / COMPAQ HSV*). > Doesnt that just failover the LUN with the START? I think you'd end up with all LUNs active on which ever controller you scanned last. This may not be ideal. And that wouldn't work for a (misconfigured) CLARiiON anyway, I think. > Wasn't this flag in part motivated by the lack of multipath support > anyway ? > > Even in a cluster context, I don't really buy the annoyance of > occasional LUN ping-pong. > This is very possible. You can bring many active/passive arrays to their knees if you flip it back and forth under load. Although, I don't see that this is specifc to the READ_CAPACITY issue. Cheers, Phil > regards, > -- > christophe varoqui > > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Philip R. Auld, Ph.D. Egenera, Inc. Software Architect 165 Forest St. (508) 858-2628 Marlboro, MA 01752