Thanks David, something new to look into. Bobby Bauer Center for Information Technology National Institutes of Health Bethesda, MD 20892-5628 301-594-7474
-----Original Message----- From: David Boyes [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 12, 2008 1:37 PM To: [email protected] Subject: Re: Safety Reminder: If you are planning disk upgrades, make sure you switch your Linux guests to by-path IDs in /etc/fstab BEFORE you switch > I'm new enough to ask. What? The basic problem is that the by-ID disk references are generated based on the PHYSICAL disk media, and are unique to that alone. On a system where disk = physical media (like Intel), this marginally makes sense, but on environments like s390x where you have multiple logical disks on the same physical disk, all the logical disks GET THE SAME by-ID REFERENCE, ie, all minidisks on the same physical volume get the same by-ID reference value. If you move the virtual machine minidisks to another volume, the by-ID reference is no longer valid, and the machine fails to boot. If you create another minidisk on the same volume and attach it to a virtual machine, the kernel cannot distinguish between the two disks, and will fail to mount one properly. If you replace the disk subsystem with new disks, ALL the by-ID references fail, as the physical media ID is no longer the same. For some (insane) reason, at least one of the major vendors chose by-ID as the default method for referring to disks during the install process, and generates by-ID references in /etc/fstab as part of that process. Some ISVs also use the by-ID syntax in their "recommended" configurations. You're affected if any line in your /etc/fstab contains the string 'by-id' in any case (upper, lower, or mixed). Replacing this by the 'by-path' syntax allows you to accomplish the same effect of uniquely identifying a logical disk address and getting it assigned the same device and filesystem mount point. It tolerates changes in disk hardware, and is cloning friendly. If you use YaST or other similar tools to add disk, use Device Path when adding them, and use Device Path during installs if you can. I'm chasing down whether this is something that can be specified in an autoyast file (I think so, but don't know the precise syntax). > > Bobby Bauer > Center for Information Technology > National Institutes of Health > Bethesda, MD 20892-5628 > 301-594-7474 > > > > -----Original Message----- > From: Stephen Frazier [mailto:[EMAIL PROTECTED] > Sent: Tuesday, August 12, 2008 12:47 PM > To: [email protected] > Subject: Re: Safety Reminder: If you are planning disk upgrades, make > sure you switch your Linux guests to by-path IDs in /etc/fstab BEFORE > you switch > > Two questions that anyone who is new enough to need your reminder will > ask are: > > What default do you suggest? > When changing it, how should it be changed? > > The old timers here will know the answers. > > David Boyes wrote: > > A safety reminder: If you're planning to replace disk subsystems, make > > > sure your Linux guests (particularly any SLES 10 or above) guests do > NOT > > use by-ID paths in /etc/fstab. Fix this BEFORE the new disk goes in, > > both RH and SuSE (Debian, too), or your guests will not be able to > find > > their filesystems (and thus won't boot or run). > > > > > > > > This really should be in IBM and other DASD vendors planning > information > > for new installs, and I'd demand a fix from your Linux vendors. By-ID > is > > a stupid default for this architecture (for any architecture, I'd > > argue...) and needs a fix ASAP. > > > > > > > > IBM, EMC, Hitachi: how do we get this added to your planning guides? > RH, > > Novell, how about it? > > > > > > > > -- db > > > > > > > > -- > Stephen Frazier > Information Technology Unit > Oklahoma Department of Corrections > 3400 Martin Luther King > Oklahoma City, Ok, 73111-4298 > Tel.: (405) 425-2549 > Fax: (405) 425-2554 > Pager: (405) 690-1828 > email: stevef%doc.state.ok.us
