Re: [linux-lvm] How to handle Bad Block relocation with LVM?

[Stuart D Gathman <stuart@bmsi.com>]

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Long ago, Nostradamus foresaw that on 11/28/2012 08:57 AM, Zdenek
Kabelac would write:
>
>> To resurrect a really, really, old thread, did anything ever get done
>> in LVM2
>> to either automatically or manually map out PEs with bad blocks in them?
>>
>> Does anyone have a recipe for doing this -- to save me the time of
>> figuring it
>> all out for myself?
>
>
> Sorry, no automated tool.
>
> You could possibly pvmove separated PEs manually with set of pvmove
> commands.
> But I'd strongly recommend to get rid of such broken driver quickly
> then you loose any more data - IMHO it's the most efficient solution
> cost & time.
There are many situations where you are out with a laptop in a region
where there is no Fry's to purchase a new drive.  Often, such region
additionally impose stiff duties, many times the price, if you try to
order said drive online.  That's assuming internet is usable today in
said region.

So "replace the drive" might the best policy ideally, but is often
impossible for travellers in tech-primitive regions.

Having helped people in such situations (where internet at least was
working), I've used the attached script to help find affected LVs and files.

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#!/usr/bin/python
# Identify partition, LV, file containing a sector 

# Copyright (C) 2010,2012 Stuart D. Gathman
# Shared under GNU Public License v2 or later
#   This program is free software; you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation; either version 2 of the License, or
#   (at your option) any later version.

#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.

#   You should have received a copy of the GNU General Public License along
#   with this program; if not, write to the Free Software Foundation, Inc.,
#   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

import sys
from subprocess import Popen,PIPE

ID_LVM = 0x8e
ID_LINUX = 0x83
ID_EXT = 0x05
ID_RAID = 0xfd

def idtoname(id):
  if id == ID_LVM: return "Linux LVM"
  if id == ID_LINUX: return "Linux Filesystem"
  if id == ID_EXT: return "Extended Partition"
  if id == ID_RAID: return "Software RAID"
  return hex(id)

class Segment(object):
  __slots__ = ('pe1st','pelst','lvpath','le1st','lelst')
  def __init__(self,pe1st,pelst):
    self.pe1st = pe1st;
    self.pelst = pelst;
  def __str__(self):
    return "Seg:%d-%d:%s:%d-%d" % (
      self.pe1st,self.pelst,self.lvpath,self.le1st,self.lelst)

def cmdoutput(cmd):
  p = Popen(cmd, shell=True, stdout=PIPE)
  try:
    for ln in p.stdout:
      yield ln
  finally:
    p.stdout.close()
    p.wait()

def icheck(fs,blk):
  "Return inum from block number, or 0 if free space."
  for ln in cmdoutput("debugfs -R 'icheck %d' '%s' 2>/dev/null"%(blk,fs)):
    b,i = ln.strip().split(None,1)
    if not b[0].isdigit(): continue
    if int(b) == blk:
      if i.startswith('<'):
	return 0
      return int(i)
  raise ValueError('%s: invalid block: %d'%(fs,blk))

def ncheck(fs,inum):
  "Return filename from inode number, or None if not linked."
  for ln in cmdoutput("debugfs -R 'ncheck %d' '%s' 2>/dev/null"%(inum,fs)):
    i,n = ln.strip().split(None,1)
    if not i[0].isdigit(): continue
    if int(i) == inum:
      return n
  return None

def blkid(fs):
  "Return dictionary of block device attributes"
  d = {}
  for ln in cmdoutput("blkid -o export '%s'"%fs):
    k,v = ln.strip().split('=',1)
    d[k] = v
  return d

def getpvmap(pv):
  pe_start = 192 * 2
  pe_size = None
  seg = None
  segs = []
  for ln in cmdoutput("pvdisplay --units k -m %s"%pv):
    a = ln.strip().split()
    if not a: continue
    if a[0] == 'Physical' and a[4].endswith(':'):
      pe1st = int(a[2])
      pelst = int(a[4][:-1])
      seg = Segment(pe1st,pelst)
    elif seg and a[0] == 'Logical':
      if a[1] == 'volume':
	seg.lvpath = a[2]
      elif a[1] == 'extents':
	seg.le1st = int(a[2])
	seg.lelst = int(a[4])
	segs.append(seg)
    elif a[0] == 'PE' and a[1] == 'Size':
      if a[2] == "(KByte)":
	pe_size = int(a[3]) * 2
      elif a[3] == 'KiB':
	pe_size = int(float(a[2])) * 2
  if segs:
    for ln in cmdoutput("pvs --units k -o+pe_start %s"%pv):
      a = ln.split()
      if a[0] == pv:
        lst = a[-1]
	if lst.lower().endswith('k'):
	  pe_start = int(float(lst[:-1]))*2
	  return pe_start,pe_size,segs
  return None

def findlv(pv,sect):
  res = getpvmap(pv)
  if not res: return None
  pe_start,pe_size,m = res
  if sect < pe_start:
    raise Exception("Bad sector in PV metadata area")
  pe = int((sect - pe_start)/pe_size)
  pebeg = pe * pe_size + pe_start
  peoff = sect - pebeg
  for s in m:
    if s.pe1st <= pe <= s.pelst:
      le = s.le1st + pe - s.pe1st
      return s.lvpath,le * pe_size + peoff

def getmdmap():
  with open('/proc/mdstat','rt') as fp:
    m = []
    for ln in fp:
      if ln.startswith('md'):
	a = ln.split(':')
	raid = a[0].strip()
	devs = []
	a = a[1].split()
	for d in a[2:]:
	  devs.append(d.split('[')[0])
	m.append((raid,devs))
    return m

def parse_sfdisk(s):
  for ln in s:
    try:
      part,desc = ln.split(':')
      if part.startswith('/dev/'):
        d = {}
        for p in desc.split(','):
	  name,val = p.split('=')
	  name = name.strip()
	  if name.lower() == 'id':
	    d[name] = int(val,16)
	  else:
	    d[name] = int(val)
	yield part.strip(),d
    except ValueError:
      continue

def findpart(wd,lba):
  s = cmdoutput("sfdisk -d %s"%wd)
  parts = [ (part,d['start'],d['size'],d['Id']) for part,d in parse_sfdisk(s) ]
  for part,start,sz,Id in parts:
    if Id == ID_EXT: continue
    if start <= lba < start + sz:
      return part,lba - start,Id
  return None

if __name__ == '__main__':
  wd = sys.argv[1]
  lba = int(sys.argv[2])
  print wd,lba,"Whole Disk"
  res = findpart(wd,lba)
  if not res:
    print "LBA is outside any partition"
    sys.exit(1)
  part,sect,Id = res
  print part,sect,idtoname(Id)
  if Id == ID_LVM:
    bd,sect = findlv(part,sect)
    # FIXME: problems if LV is snapshot
  elif Id == ID_LINUX:
    bd = part
  else:
    if Id == ID_RAID:
      for md,devs in getmdmap():
	for dev in devs:
	  if part == "/dev/"+dev:
	    part = "/dev/"+md
	    break
        else: continue
	break
    res = findlv(part,sect)
    if res:
      print "PV =",part
      bd,sect = res
    else:
      bd = part
  blksiz = 4096
  blk = int(sect * 512 / blksiz)
  p = blkid(bd)
  try:
    t = p['TYPE']
  except:
    print bd,p
    raise
  print "fs=%s block=%d %s"%(bd,blk,t)
  if t.startswith('ext'):
    inum = icheck(bd,blk)
    if inum:
      fn = ncheck(bd,inum)
      print "file=%s inum=%d"%(fn,inum)
    else:
      print "<free space>"