From mboxrd@z Thu Jan 1 00:00:00 1970 From: Luca Berra Subject: Re: RFC - device names and mdadm with some reference to udev. Date: Sun, 2 Nov 2008 14:47:07 +0100 Message-ID: <20081102134707.GA21279@maude.comedia.it> References: <18692.62860.863118.727187@notabene.brown> <1225387127.26510.155.camel@firewall.xsintricity.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Return-path: Content-Disposition: inline In-Reply-To: <1225387127.26510.155.camel@firewall.xsintricity.com> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, Oct 30, 2008 at 01:18:47PM -0400, Doug Ledford wrote: >> 4/ auto-assembly needs to do the right thing on a SAN where multiple >> hosts can each see multiple arrays. Clearly only one host should >> write to any one array at one time (until I get some >> cluster-awareness going, which I had hoped to work on this year, >> but it doesn't look like I will). >> In this case, I don't think read-auto is enough. We either need >> to not assemble arrays when aren't known to belong to us, or we >> need to assemble them read-only and require and explicit >> read-write setting. >> >> So we need some way to know which devices could be visible to >> other hosts. >> I could have a global flag in mdadm.conf "Options SAN" >> I could have a SAN-DEVICES to match "DEVICES", but as just about >> everything is "/dev/sd*" these days, I don't know if that would >> work. >> >> Any suggestions concerning this would be welcome. > >The scariest suggestion, but probably the most complete and automated, >would be to have mdadm do a search on any constituent devices to find >out what the eventual low level driver is. If it's a fiber channel >driver, or iSCSI, then don't auto assemble. If it's sata/e-sata, or >local SAS, then it's more likely auto assemble is fine. But, that level >of mucking around in /sys for each device would probably be quite ugly. > unfortunately this will not work out correctly 1) it is fairly possible for an host to boot from fiber-channel, and to run md over it (it is a fairly common setup here). 2) scsi supports shared storage, and i believe SAS does too. L. -- Luca Berra -- bluca@comedia.it Communication Media & Services S.r.l. /"\ \ / ASCII RIBBON CAMPAIGN X AGAINST HTML MAIL / \