[Info-vax] Transient anal/disk errors

[tadamsmar]

On Thursday, December 12, 2013 11:31:44 AM UTC-5, Stephen Hoffman wrote:
> On 2013-12-12 15:51:16 +0000, tadamsmar said:
> 
> 
> 
> > On Thursday, December 12, 2013 10:07:28 AM UTC-5, Stephen Hoffman wrote:
> 
> >> There's also the infamous BACKUP /IGNORE=INTERLOCK command, which 
> 
> >> some>> folks think is an online BACKUP.  It's not.  Worse, it allows 
> 
> >> silent>> data corruptions in the output savesets.  If you have control 
> 
> >> over the>> applications involved, that's where the BACKUP support needs 
> 
> >> to reside,>> particularly if your applications are writing clumps of 
> 
> >> updates to>> disk.  Various relational databases on VMS include 
> 
> >> application-internal>> backup tools, and always use those in preference 
> 
> >> to using the OpenVMS>> BACKUP command.  Alternatively, quiesce the 
> 
> >> applications or the disks>> or the systems, and then use the standard 
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> >> BACKUP tools. Or quiesce the>> environment and yank a disk from the 
> 
> >> shadowset, and backup that.
> 
> > 
> 
> > You think I was recently working on my backup strategy?  I was just 
> 
> > working on those persistent ANAL/DISK problems.
> 
> 
> 
> Yes, so was I.  In my admittedly skewed view of the world, 
> 
> investigations of persistent disk errors are always secondary to having 
> 
> good and verified backups.  Preserve the most current data first, then 
> 
> study the disks and the errors.
> 
> 
> 
> > But I probably do need to work on my backup strategy.  I have been 
> 
> > yanking out a disk without quiescing and backing up the yanked disk, 
> 
> > and I have not done any deliberate recovery testing, just defacto when 
> 
> > I had to recover a file or compress a disk.  Just yanking a disk is 
> 
> > easy, I just have to run command procedures, but as you point out, it 
> 
> > might not have optimal reliability.
> 
> 
> 
> You're hot-plugging active disks,

By "yanking" I just meant dismounting a disk from a shadowset.  We only have one system, the AS800, that allow literal yanking of a physical disk.

> and probably in an environment 
> 
> without a quiesce function on the storage controller?
> 
> 
> 
> Don't do that.
> 
> 
> 
> You've probably been causing some of the errors and corruptions here.
> 
> 
> 
> > What's the easiest way to quiesce and yank?
> 
> 
> 
> Depending on the bus and the target, via DISMOUNT command.  Some 
> 
> storage controllers support a quiesce function, and others expect you 
> 
> to shut down.  I'm guessing your gear probably lacks one of those 
> 
> controllers; that feature usually only exists on outboard storage 
> 
> controllers.  It's not a feature usually found with host-based JBOB 
> 
> SCSI controllers, nor even necessarily on some of the host-based SCSI 
> 
> RAID controllers.
> 
>
dismount is what I meant by yank. 
> 
> But that's not how I'd do the backups I'm referring to.  I'd DISMOUNT 
> 
> the disk from the shadowset, and MOUNT /NOWRITE the disk privately, and 
> 
> back up from there.  There are minimerge and minicopy bitmaps that were 
> 
> discussed here in massive detail when Phillip Helbig was trying to 
> 
> understand how all that worked, so I'm not going to bother reposting 
> 
> all of that here.  Those features will help bring the 
> 
> temporarily-removed disk back to current within the shadowset more 
> 
> quickly.   Search for threads with minicopy or minimerge or related 
> 
> keywords via Google Groups, and start reading.  Or check the current 
> 
> volume shadowing manual in the OpenVMS documentation set.  Or both.
> 

I use /minicopy when I dismount for backing up.

> 
> 
> > The only way I am sure of is to shutdown, boot with a CD, yank, then 
> 
> > reboot normally.
> 
> 
> 
> That's the best way, official way, and only supported way, if you need 
> 
> to reconfigure a SCSI, and lack a storage controller with a quiesce 
> 
> function.
> 
> 
> 
> > I am not sure that there is a console command that will yank a disk 
> 
> > from a shadowset, but I seem to recall one that will disable shadowing.
> 
> 
> 
> Allow me to translate "I don't recall" as "which manual should I read 
> 
> to learn more about the fundamental operations of the server?".  That'd 
> 
> be the volume shadowing manual.    <http://www.hp.com/go/openvms/doc>, 
> 
> select the VMS documentation shelf, and search for "shadowing", and 
> 
> skim that manual.  You'll definitely need to be more familiar with it 
> 
> if (when?) you decide to implement minicopy or minimerge.  (Though your 
> 
> VMS version is ancient, and there were definitely various patches made 
> 
> available in this and related areas of OpenVMS.)
> 
> 
> 
> > I have noticed that sometimes a yanked disk will not run ANAL/DISK 
> 
> > clean. This also seems to be transient.
> 
> 
> 
> Yeah.  Sometimes yanking the disk just silently corrupts the file data 
> 
> on that disk, depending on the timing.  I wouldn't assume other disks 
> 
> on the SCSI bus would be entirely immune from problems or corruptions, 
> 
> either.  Not without quiescing the bus, or shutting down, or 
> 
> dismounting the disks on that bus.
> 
> 

I meant dismounting. If I dismount from a shadowset and run anal/disk on the dismounted disk, I sometimes get warnings form anal/disk.  I just recently started checking this as I have gotten a bit more concerned after I had persistent warnings from anal/disk on one system that required a good bit of cleanup.

So perhaps even a dismount from a shadowset is a bit risky for backing up.  Of course, it's a heck of a lot easier than the official way to prep a disk for backup.

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