Re: [Xen-users] how to start VMs in a particular order

[Adam Goryachev <mailinglists@xxxxxxxxxxxxxxxxxxxxxx>]

On 30/06/14 17:11, Joost Roeleveld wrote:
> On Sunday 29 June 2014 17:35:17 lee wrote:
> > "J. Roeleveld" <joost@xxxxxxxxxxxx> writes:
> > > On Sunday, June 29, 2014 10:09:32 AM lee wrote:
> > > > > Quite possibly. Am I correct in assuming you are using old hardware
> > > > > with
> > > > > closed-source software?
> > > > It's an IBM x3650 7979 L2G with a ServeRaid 8k.  Arcconf seems to be
> > > > closed source --- I don't really need arcconf, though.
> > > >
> > > > Unfortunately, disabling the status checking hasn't solved the problem.
> > > > The server goes down with messages about the SCSI bus hanging and trying
> > > > to reset it.  I suspect that the controller doesn't like the --- rather
> > > > unsuited --- WD20EARS I plugged in.  They have been working fine with a
> > > > HP smart array P800, though.  I might have to take them out to see if
> > > > the problem persists.
> > > SCSI bus hanging, sounds like an I/O issue.
> > > Try to read the SMART-values of the disk.
> > I'm not sure how to do that, and what would they tell me?
> Either connect the disks directly to a sata port on a mainboard (normal
> desktop would suffice). Disabling the raid-functionality of the card might also
> suffice.
> Then use (assuming the disk is /dev/sda)
> # smartctl --all /dev/sda
>
> > > Also, try a different disk...
> > Unfortunately, I don't have one I could try --- and I'd need three.
> >
> > > The WD20EARS is a "green" desktop disk. I had numerous issues when using a
> > > couple of those in my old server when using software raid (mdadm).
> > > Some hardware raid cards do not like disks that do not properly return
> > > error- states. And especially the green disks that have a tendency to go
> > > into powersave mode when not used for a short period of time.
> > I know, they aren't suited for this purpose.  Yet they have been working
> > fine on the P800, and that three disks should decide to go bad in a way
> > that blocks the controller (or whatever happens) every now and then
> > seems unlikely.
> No, it doesn't.
> Does the error occur after the server has been idle for a while? Or when the
> disks are being stressed?
>
> If the former, then you need to figure out how to AVOID the disks to enter
> powersaving mode. It takes time for the disks to spin up again afterwards. The
> raid controller is timing out on access to the disks.
>
> If the latter, then you might have issues on the drives themselves which the
> drives are trying to solve themselves.
>
> My guess is that it is the former. (eg. when the server has been idle for a
> while)
BTW, this reminds me of the issue of these type of disks (consumer/non 
RAID) dropping out of linux MD raid arrays by themselves, even though 
they are perfectly good. For the cause, and solution, read up on SCT/ERC.
BTW, google for sct/erc and result 4 (for me) talks about WD releasing 
the red line for use in RAID. The short story is that the green disk 
will try (really hard) to get the data in a requested sector (because it 
is probably the only location the user has saved this important data), 
and ignore any instructions from the raid controller. Since this can 
take a few minutes, then the raid controller has decided the drive is 
dead (usually I read about this that Linux decides the disk is dead and 
marks it as failed for the raid array).
In Linux software raid, the solution is to tell the kernel to be more 
patient, and wait longer for the disk to respond, so it doesn't get 
kicked out of the array, with hardware raid, you may not have that option.
In RAID drives (like the red, or enterprise level), if a sector is not 
readable (quickly, about 6 seconds I think), then the drive will simply 
return an error, assuming that MD or hardware raid controller will 
simply read the bad sector from another disk in the array.
I hope this helps...

BTW, with current size drives, it is common/frequent to have the above 
issue. Sometimes even a single complete read of the drive can trigger 
it, see linux-raid mailing list for more information.
Regards,
Adam

--
Adam Goryachev Website Managers www.websitemanagers.com.au

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