getting pe_start right

While trying to convert my mdadm raid5 array from metadata format 0.9 to 1.0, I forgot to specify the version and it defaulted to 1.2, which damaged the lvm metadata. After correcting mdadm to 1.0, I decided to try to recreate the LVM after managing to locate the volume descriptions in the metadata after manually dumping it.

The problem I now have is that pvcreate will not use the same pe_start as before. It was 384 and it is now 3072. I tried using --metadatasize 192k --dataalignmentsize 0 and it did not help. What gives?

Try "--metadatasize 288k

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Phillip Susi
Sent: Friday, May 06, 2011 10:56 AM
To: [email protected]
Subject: [linux-lvm] getting pe_start right

While trying to convert my mdadm raid5 array from metadata format 0.9 to

1.0, I forgot to specify the version and it defaulted to 1.2, which damaged the lvm metadata. After correcting mdadm to 1.0, I decided to try to recreate the LVM after managing to locate the volume descriptions

in the metadata after manually dumping it.

The problem I now have is that pvcreate will not use the same pe_start as before. It was 384 and it is now 3072. I tried using --metadatasize

192k --dataalignmentsize 0 and it did not help. What gives?

_______________________________________________
linux-lvm mailing list
[email protected]
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Try to set
default_data_alignment = 0

from lvm.conf:
# Default alignment of the start of a data area in MB. If set to 0,

# a value of 64KB will be used.  Set to 1 for 1MiB, 2 for 2MiB, etc.

Also, if you use

	pvcreate --uuid <pv uuid from metadata> --restorefile <old VG backup>

it should create PV exacltly as needed for olf VG (with --restorefile it uses offset from metadata backup, overriding default)

Then vgcfgrestore and you should have exactly the same cfg.

Milan

Would be quite helpful if you shared kernel and lvm2 version info...

chances are lvm2's data_alignment_detection will shift the data start to the start of the next full stripe of the raid5.

You should be able to specify the old start with:

--dataalignment 192k --dataalignmentoffset 0

(--dataalignmentoffset 0 likely isn't needed, but it just overrides lvm2's data_alignment_offset detection if it just so happens that raid5 has alignment_offset!=0)

That appears to be what was going on. I found entries in lvm.conf to enable/disable autodetection of the raid stripe width and turned it off.

The command line switches did not appear to override the autodetection; I had to shut it off in the conf file. Is this a bug?