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TSKVolumeSystem bytes_per_sector #45

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#822
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TSKVolumeSystem bytes_per_sector#45
#822
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joachimmetz
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enhancementquestionThis issue is a question

Description

@forensicmatt
forensicmatt
opened on Jul 21, 2015

I have a drive that has geometry with 4096 bytes per sector.

When I create a TSKVolumeSystem, and feed it the volume_system_path_spec of TYPE_INDICATOR_TSK_PARTITION, it shows that the TSKVolumeSystem.bytes_per_sector attribute as 512. This interns shows the incorrect offset for the partitions.

Is there a way to find and set the bytes per sector for a TSKVolumeSystem?

Here is what FTK Imager shows for the drive:
image

Partition Start Sector [2048]:
image

Offset then to partition is 2048 * 4096 = 8388608

I see in dfvfs TSKVolumeSystem._Parse() there is:
self.bytes_per_sector = tsk_partition.TSKVolumeGetBytesPerSector(tsk_volume)

Am I not passing something or are the BytesPerSector not being found correctly?

Here is output and an example code I used.

###########################################################
#Output 
###########################################################
bytes_per_sector: 512
address: 2; description: NTFS (0x07); offset: 1048576; size 250048817664

###########################################################
#Example 
###########################################################

import sys
from dfvfs.path import factory as path_spec_factory
from dfvfs.lib import definitions as dfvfs_definitions
from dfvfs.volume import tsk_volume_system

from dfvfs.lib import tsk_image

os_path_spec = path_spec_factory.Factory.NewPathSpec(
    dfvfs_definitions.TYPE_INDICATOR_OS,
    location='\\\\.\\PHYSICALDRIVE1'
)

volume_system_path_spec = path_spec_factory.Factory.NewPathSpec(
    dfvfs_definitions.TYPE_INDICATOR_TSK_PARTITION,
    start_offset=0,
    parent=os_path_spec
)

image_system = tsk_volume_system.TSKVolumeSystem()
image_system.Open(volume_system_path_spec)

print 'bytes_per_sector: {}'.format(image_system.bytes_per_sector)

for volume in image_system.volumes:
    volume_identifier = getattr(volume, 'identifier', None)
    if volume_identifier:
        info = {}
        for attrib in volume.attributes:
            info[attrib.identifier] = attrib.value
        for extent in volume.extents:
            info['offset'] = extent.offset
            info['size'] = extent.size

        print 'address: {}; description: {}; offset: {}; size {}'.format(info['address'],info['description'],info['offset'],info['size'])

Activity

  1. joachimmetz
    added
    questionThis issue is a question
    enhancement
    on Jul 22, 2015

  2. joachimmetz commented on Jul 22, 2015

    @joachimmetz
    joachimmetz
    on Jul 22, 2015
    Member
    Is there a way to find and set the bytes per sector for a TSKVolumeSystem?

    Not at the moment. I would also need to check if and how that can be propagated in pytsk and TSK.

    os_path_spec = path_spec_factory.Factory.NewPathSpec(
    dfvfs_definitions.TYPE_INDICATOR_OS,
    location='\\\\.\\PHYSICALDRIVE1'
)

    Since Python os does not support \.\PhysicalDrive1 as a file, dfvfs TYPE_INDICATOR_OS uses pysmdev instead. Also see: https://github.com/log2timeline/dfvfs/blob/master/dfvfs/file_io/os_file_io.py#L65

    Hence try:

    import pysmdev
smdev_handle = pysmdev.handle()
smdev_handle.open('\\\\.\\PHYSICALDRIVE1')
print(smdev_handle.bytes_per_sector)
smdev_handle.close()
  3. joachimmetz
    self-assigned this
    on Jul 22, 2015

  4. joachimmetz commented on Jan 21, 2022

    @joachimmetz
    joachimmetz
    on Jan 21, 2022
    Member

    Generated a 4k MBR test image

    mmls test_data/mbr_4k_sector.raw 
DOS Partition Table
Offset Sector: 0
Units are in 512-byte sectors

      Slot      Start        End          Length       Description
000:  Meta      0000000000   0000000000   0000000001   Primary Table (#0)
001:  -------   0000000000   0000000000   0000000001   Unallocated
002:  000:000   0000000001   0000000017   0000000017   Linux (0x83)
003:  Meta      0000000018   0000001023   0000001006   DOS Extended (0x05)
004:  -------   0000000018   0000008191   0000008174   Unallocated

    By default mmls (and therefore assuming libtsk/pytsk as well) this as 512 bytes per sector. With a manual override:

    mmls -b 4096 test_data/mbr_4k_sector.raw 
DOS Partition Table
Offset Sector: 0
Units are in 4096-byte sectors

      Slot      Start        End          Length       Description
000:  Meta      0000000000   0000000000   0000000001   Primary Table (#0)
001:  -------   0000000000   0000000000   0000000001   Unallocated
002:  000:000   0000000001   0000000017   0000000017   Linux (0x83)
003:  Meta      0000000018   0000001023   0000001006   DOS Extended (0x05)
004:  Meta      0000000018   0000000018   0000000001   Extended Table (#1)
005:  -------   0000000018   0000000018   0000000001   Unallocated
006:  001:000   0000000019   0000000035   0000000017   Linux (0x83)
007:  -------   0000000036   0000001023   0000000988   Unallocated

    To consider:

    • support manual override of sector size?
    • add sector size detection in dfVFS to work around limitation in libtsk/pytsk?
    • alternative MBR support also see Improve volume system support #83

  5. joachimmetz commented on Jan 21, 2022

    @joachimmetz
    joachimmetz
    on Jan 21, 2022
    Member

    Looks like sleuthkit has a long standing issue about this sleuthkit/sleuthkit#752

  6. joachimmetz commented on Jul 15, 2026

    @joachimmetz
    joachimmetz
    on Jul 15, 2026
    Member

    changes to allow pytsk to set sector size https://github.com/py4n6/pytsk/pull/149/changes via Img_Info constructor

  7. joachimmetz commented on Jul 15, 2026

    @joachimmetz
    joachimmetz
    on Jul 15, 2026
    Member

    Cannot use SleuthKit for reliable MBR block size detection:

    mmls -b 4096 test_data/mbr.raw 
DOS Partition Table
Offset Sector: 0
Units are in 4096-byte sectors

      Slot      Start        End          Length       Description
000:  Meta      0000000000   0000000000   0000000001   Primary Table (#0)
001:  -------   0000000000   0000000000   0000000001   Unallocated
002:  000:000   0000000001   0000000129   0000000129   Linux (0x83)
003:  Meta      0000000130   0000008191   0000008062   DOS Extended (0x05)
004:  -------   0000000130   0000001023   0000000894   Unallocated

    For reliable detection this should fail

    mmls test_data/mbr.raw 
DOS Partition Table
Offset Sector: 0
Units are in 512-byte sectors

      Slot      Start        End          Length       Description
000:  Meta      0000000000   0000000000   0000000001   Primary Table (#0)
001:  -------   0000000000   0000000000   0000000001   Unallocated
002:  000:000   0000000001   0000000129   0000000129   Linux (0x83)
003:  Meta      0000000130   0000008191   0000008062   DOS Extended (0x05)
004:  Meta      0000000130   0000000130   0000000001   Extended Table (#1)
005:  -------   0000000130   0000000130   0000000001   Unallocated
006:  001:000   0000000131   0000000259   0000000129   Linux (0x83)
007:  -------   0000000260   0000008191   0000007932   Unallocated

  8. joachimmetz commented on Jul 15, 2026

    @joachimmetz
    joachimmetz
    on Jul 15, 2026
    Member

    Alternative option is to add sector_size to SourceScanner - this might be also needed as fallback for situation where the sector size cannot be detected

  9. joachimmetz
    linked a pull request that will close this issueChanges to support non 512 block sizes with TSK partition #822on Jul 17, 2026
  10. joachimmetz
    closed this as completedin #822on Jul 17, 2026

  11. joachimmetz commented on Jul 17, 2026

    @joachimmetz
    joachimmetz
    on Jul 17, 2026
    Member

    Changes in #822 to set sector_size manually

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