Re: recovering from raid5 corruption

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On Sun, 29 Apr 2012 19:29:10 -0400 Shaya Potter <spotter@xxxxxxxxx> wrote:

> On 04/29/2012 06:52 PM, NeilBrown wrote:
> >
> > You've written a new superblock 4K in to each device, where previously here
> > was something.   So you have probably corrupted something though we cannot
> > easily tell what.
> >
> > Retry your experiment with --metadata=0.90.  Hopefully one of those
> > combinations will work better.  If it does, make a backup of the data you
> > want to keep, then I would suggest rebuilding the array from scratch.
> 
> ok, thanks, that was a huge help.
> 
> I have it setup correctly now (obvious due to the fact that I can read 
> the lvm configuration without any gibberish when ordered correctly).

I should add that this only proves that you have the first device correct,
the rest may be wrong.
You need to activate the LVM, then look at the filesystem and see if it is
consistent before you can be sure that all devices are in the correct
position.

NeilBrown



> 
> however, now I need to figure out how to recreate the lvm appropriately. 
>   I see the configuration "file" in at the start of the raid array (less 
> -f /dev/md0 which I'm including below)
> 
> I asusme there should be a way to reuse this data to recreate the lvm?
> 
> any continued advice would be appreciated, googling doesn't seem to come 
> up with much if one doesn't have a backup of the lvm data.
> 
> raid5 {
> id = "8r27WQ-HvIw-0RQV-aksr-LJGN-DLVD-1WBg8h"
> seqno = 6
> status = ["RESIZEABLE", "READ", "WRITE"]
> extent_size = 8192
> max_lv = 0
> max_pv = 0
> 
> physical_volumes {
> 
> pv0 {
> id = "7P0W3p-XoPg-rCo8-HJ2G-Hfxc-UDWI-x6nQck"
> device = "/dev/md0"
> 
> status = ["ALLOCATABLE"]
> dev_size = 11721107456
> pe_start = 384
> pe_count = 1430799
> }
> }
> 
> logical_volumes {
> 
> data {
> id = "YZvrHt-Glyr-wnj0-QzV1-qRe6-VcRH-D7wU3U"
> status = ["READ", "WRITE", "VISIBLE"]
> segment_count = 1
> 
> segment1 {
> start_extent = 0
> extent_count = 524288
> 
> type = "striped"
> stripe_count = 1        # linear
> 
> stripes = [
> "pv0", 0
> ]
> }
> }
> 
> image {
> id = "uHOzpc-l8L7-eF5h-Fa0C-EsCS-sM6X-3GpOP0"
> status = ["READ", "WRITE", "VISIBLE"]
> segment_count = 1
> 
> segment1 {
> start_extent = 0
> extent_count = 906511
> 
> type = "striped"
> stripe_count = 1        # linear
> stripes = [
> "pv0", 524288
> ]
> }
> }
> }
> }
> # Generated by LVM2 version 2.02.39 (2008-06-27): Wed Aug 19 23:36:50 2009
> 
> contents = "Text Format Volume Group"
> version = 1
> 
> description = ""
> 
> creation_host = "nas"   # Linux nas 2.6.27-14-generic #1 SMP Fri Jul 24 
> 22:19:33 UTC 2009 i686
> creation_time = 1250739410      # Wed Aug 19 23:36:50 2009

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