Difference between revisions of "Badblocks"

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  # mkfs.<filesystem-type> '''-l''' /root/<badblocks.txt> /dev/<device>
 
  # mkfs.<filesystem-type> '''-l''' /root/<badblocks.txt> /dev/<device>
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{{Note|The means of {{ic|0/0/527405}} errors is <number of read errors>/<number of write errors>/<number of corruption errors>.}}
  
 
==== Block size ====
 
==== Block size ====

Revision as of 23:57, 13 January 2013

badblocks is a program to test storage devices for bad blocks.

In case of a HDD the whole sector should get retired. A sector is a subdivision of a track on a storage device and sectors that have become bad cannot be used because they have become permanently damaged (a bad sector can change a letter in a text file to causing a binary program to have a segmentation fault).

S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) is Hardware-featured in almost every HDD still in use nowadays and in some cases it can automatically retire defect HDD Sectors. Anyhow it only passively waits for errors while badblocks writes simple patterns to every block of a device and then reads and checks them searching for damaged areas. (Just like memtest86* does with RAM.)

This can be done in a destructive write-mode that effectively wipes the device (do Backup!) or in non-destructive read-write (Backup advisable as well!) and read-only modes.

Usage

badblocks is in e2fsprogs

Usage:

badblocks  [  -svwnfBX  ]  [  -b  block-size  ] [ -c blocks_at_once ] [ -e max_bad_blocks ]
[ -d read_delay_factor ] [ -i input_file ] [ -o output_file ] [ -p num_passes ] [ -t test_pattern ]
device [ last-block ] [ first-block ]

Storage Device Fidelity

Although there is no firm rule has been set, it is common thinking that a new drive should have zero bad sectors. Over time, bad sectors will develop on a storage device and although they are able to be defined to the file system so that they are avoided, continual use of the drive will usually result in additional bad sectors forming and are usually the harbinger of death of a hard drive. Replacement of the device is recommended.

Comparisons with Other Programs

Typical recommended practice for testing a storage device for bad sectors is to use the manufacturer's testing program. Most manufacturers have programs that do this. The main reasoning for this is that manufacturers usually have their standards built into the test programs that will tell you if the drive needs to be replaced or not. The caveat here being is that some manufacturers testing programs do not print full test results and allow a certain number of bad sectors saying only if they pass or not. Manufacturer programs, however, are generally quicker than badblocks sometimes a fair amount so.

Testing for Bad Sectors

To test for bad sectors in Linux the program badblocks is typically used. badblocks had several different modes to be able to detect bad sectors.

read-write Test

This test is primarily for testing new drives and is a read-write test. As the pattern is written to every accesible block the device effectively gets wiped. Default is an extensive test with four passes using four different patterns: 0xaa (10101010), 0x55 (01010101), 0xff (11111111) and 0x00 (00000000). For some devices this will take a couple of days to complete.

# badblocks -wsv /dev/<device>
Checking for bad blocks in read-write mode
From block 0 to 488386583
Testing with pattern 0xaa: done
Reading and comparing: done
Testing with pattern 0x55: done
Reading and comparing: done
Testing with pattern 0xff: 22.93% done, 4:09:55 elapsed. (0/0/0 errors)
[...]
Testing with pattern 0x00: done
Reading and comparing: done
Pass completed, 0 bad blocks found. (0/0/0 errors)

Options:

-w
do a destructive write test
-s
show progress-bar
-v
be "verbose" and output bad sectors detected to stdout


Additional options you might consider:

-p <number>
run through the extensive four pass test <number> of sequent iterations
-o </path/to/output-file>
print bad sectors to <output-file> instead of stdout
-t <test_pattern> 
Specify a pattern. See below.


define specific test pattern

From the manpage: "The <test_pattern> may either be a numeric value between 0 and ULONG_MAX-1 inclusive [...]."

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:Badblocks#)
random pattern

Badblocks can be made to repeatedly write a single "random pattern" with the -t random option.

# badblocks -wsv -t random /dev/<device>
Checking for bad blocks in read-write mode
From block 0 to 488386583
Testing with random pattern: done                                                 
Reading and comparing: done                                                 
Pass completed, 0 bad blocks found. (0/0/0 errors)
Warning: This is not secure for cryptographic purposes. A "random pattern" is a contradiction in itself. As badblocks does not (like urandom) apply sophisticated procedures to reuse entropy but simply repeats one "random pattern" it should not be used where random data would be needed, e.g. for block device encryption.

read-write Test (non-destructive)

This test is designed for devices with data already on them. A non-destructive read-write test does transparently backup original content before testing sectors with a single random pattern and then restoring the content from the backup. This is a single pass test and is useful as a general maintenance test.

# badblocks -nsv /dev/<device>
Checking for bad blocks in non-destructive read-write mode
From block 0 to 488386583
Checking for bad blocks (non-destructive read-write test)
Testing with random pattern: done                                                 
Pass completed, 0 bad blocks found. (0/0/0 errors)

The -n option signifies a non-destructive read-write test.

Have File System Incorporate Bad Sectors

To not use bad sectors they have to be known by the filesystem.

During Filesystem Check

Incorporating bad sectors can be done using the filesystem check utility (fsck). fsck can be told to use badblocks during a check. To do a read-write (non-destructive) test and have the bad sectors made known to the filesystem run:

# fsck -vcck /dev/<device-PARTITION>

The -cc option tells run fsck in non-destructive test mode, the -v tells fsck to show its output, and the -k option preserves old bad sectors that were detected.

To do a read-only test (not recommended):

# fsck -vck /dev/<device-PARTITION>

Before Filesystem Creation

Alternately, this can be done before filesystem creation.

If badblocks is run without the -o option bad sectors will only be printed to stdout.

Example output for read errors in the beginning of the disk:

# badblocks -wsv /dev/<drive>
[...]
Testing with pattern 0xff: done                                                 
Reading and comparing:
[...]
37584
37585 0.84% done, 7:31:08 elapsed. (0/0/527405 errors)
37586
[...]
done
Testing with pattern 0x00:
Reading and comparing:
[...]
37584
37585
[...]
done
Pass completed, 527405 bad blocks found. (0/0/527405 errors)

For comfortably passing badblocks error output to the filesystem it has to be written to a file.

# badblocks -wsv -o /root/<badblocks.txt> /dev/<device>
Checking for bad blocks in read-write mode
From block 0 to 488386583
Testing with pattern 0xaa: done
Reading and comparing:   6.36% done, 0:51 elapsed. (0/0/14713 errors)
[...]
Testing with pattern 0x00: done
Reading and comparing: done
Pass completed, 527405 bad blocks found. (0/0/527405 errors)

Then (re-)create the file system with the information:

# mkfs.<filesystem-type> -l /root/<badblocks.txt> /dev/<device>
Note: The means of 0/0/527405 errors is <number of read errors>/<number of write errors>/<number of corruption errors>.

Block size

Merge-arrows-2.pngThis article or section is a candidate for merging with Securely wipe disk#Block size.Merge-arrows-2.png

Notes: Block size alignment is not specific to this tiny section. Other Arch Wiki Articles already do cover this up. Search for it and cover everything up on a Block size page. (Discuss in Talk:Badblocks#)

first find the file systems block size. For example for ext# filesystems:

# dumpe2fs /dev/<device-PARTITION> | grep 'Block size'

feed this to badblocks:

# badblocks -b <block size>

References