[lvm-devel] [PATCH] pvcreate: check the label after writing

[Lidong Zhong]

Hi list,
> Dne 25.9.2014 v 09:52 Zdenek Kabelac napsal(a):
> > Dne 25.9.2014 v 04:20 Lidong Zhong napsal(a):
> >> Some device will place metadata area at the beginning part and writing
> >> label may fail.Take our test for example, when running pvcreate on a CDL
> >> formatted DASD device(without partition), it shows successfully create
> >> a pv, but the label is not written on the second sector and pvs shows
> >> nothing. Although it is not supposed to run lvm on dasd device, it's a
> >> friendly behavior to check the label and return error if it fails.
> >
> > Hmm - if device drive tells you - it has accepted and written some bytes
> > on your storage device - they really should be written there.
> >
> > So IMHO driver should not lie and reject write request with error ?
> >
> > Otherwise you would need to validate every single written byte by LVM ?
> >
> > Maybe DASD devices should by automatically ignored by lvm filtering
> > as unusable device for PV  (just like i.e. too small devices)
> 
> It looks like DASD device is somehow supported by 'parted'
> 
> And there are some very 'innovative' ways how to work with this device and 
> detect where the write is actually allowed/supported.
> 
> So it seems like lvm2 would need to learn those bits on how to manipulate DASD 
> devices.
> 
> And also tools like blkid then needs to look at proper places how to recognize 
> such device's signature.
> 
> Anyway - the patch you've proposed is likely not valid.
> 
> Device driver for DASD should reject write attempt to privileged disk area 
> with 'error'.
> 
> It would be probably fair to disable/ignore DASD device in lvm2 for now - 
> since we clearly do not understand layout of this device and try to store PV 
> header into wrong place - and someone needs to write handled for this devices 
> to reenable support for it.
> 
That's reasonable. we added DASD device in the filter to fix this
problem.
Thank you

> There is BZ http://bugzilla.redhat.com/show_bug.cgi?id=1058326
> which is likely related to the same issue.
> 
> Zdenek
> 
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-- 
Best regards,
Lidong