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--- linux:debian:map-lba [2022/10/01 06:23] – oscar
+++ linux:debian:map-lba [Unknown date] (current) – removed - external edit (Unknown date) 127.0.0.1
@@ Line 1: / Line 1: @@
-====== Map LBA to File ======
-You might see something like this on your console / dmesg:
-<code>
-[  394.051961] end_request: I/O error, dev sda, sector 128999424
-[  394.055674] Buffer I/O error on device sda3, logical block 8800768
-</code>
-In this situation you can use the following assumptions:
-* The bad sector / LBA is 128999424 (L)
-* The bad block is 8800768 in the filesystem on sda3 (b)
-===== How to: =====
-For this example, I'll be using the following information. The second line of the output above was not provided, we need to calculate the logical block offset first.
-**Bad LBA = 0x0a8ae67d = 176875133**
-===Find out the partition===
-<code>
-$ sudo fdisk -lu /dev/sda
-Disk /dev/sda: 500.1 GB, 500107862016 bytes
-heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
-Units = sectors of 1 * 512 = 512 bytes
-Disk identifier: 0x030818eb
-   Device Boot      Start         End      Blocks   Id  System
-/dev/sda1   *          63      409662      204800   83  Linux
-/dev/sda2          409663   168181822    83886080   83  Linux
-/dev/sda3       168181823   172376126     2097152   82  Linux swap / Solaris
-/dev/sda4       172376127   976768064   402195969   83  Linux
-</code>
-Therefore this LBA is on partition: /dev/sda4
-===Get block size of the partition===
-<code>
-$ sudo tune2fs -l /dev/sda4 | grep Block
-Block count:              100548992
-Block size:               4096
-Blocks per group:         32768
-</code>
-This partition has block size: 4096
-===Calculate the block===
-<code>
-b = (int)(((L-S)*512)/B)
-where:
-  b = File System block number
-  B = File system block size in bytes
-  L = LBA of bad sector
-  S = Starting sector of partition as shown by fdisk -lu
-</code>
-Denotes the integer part (round it DOWN to a whole number).
-<code>
-b = (int)((176875133-172376127) * 512 / 4096)
-b = (int)562375.75
-b = 562375
-</code>
-The block on this partition corresponding to this LBA is: 562375
-===Identify the file===
-Use debugfs to locate the inode stored in this block, and the file that contains that inode:
-<code>
-$ sudo debugfs
-debugfs 1.41.9 (22-Aug-2009)
-debugfs:  open /dev/sda4
-debugfs:  testb 562375
-Block 562375 marked in use
-debugfs:  icheck 562375
-Block   Inode number
-  132344
-debugfs:  ncheck 132344
-Inode   Pathname
-  /attie/banner.jpg
-debugfs:  quit
-</code>
-Or if the block appears not in use anymore:
-<code>
-$ sudo debugfs
-debugfs 1.41.9 (22-Aug-2009)
-debugfs:  open /dev/sda4
-debugfs:  testb 562375
-Block 562375 not in use
-debugfs:  quit
-</code>