I would like to know If I certain file moves on the Flash memory (internal storage), between writes/updates to it.

Is there some way I can get the file's location on the Flash memory?
(Cluster Number, Sector Number, etc)

I am using Android v8,
and can either install use an App for that,
or use the Command Line, If a relevant command exists in the Linux command-prompt that Android has.


1 Answer 1


I assume by saying cluster you mean Windows' allocation unit, commonly called block in Linux world. It's a unit of data storage a filesystem uses. A cluster/block may consist of or correspond to multiple sectors on underlying storage media (HDD or flash storage). Sector is the minimum atomic unit of storage an OS can read or write. Block size is decided at the time of filesystem creation i.e. when we format a partition (high-level formatting). Partitions and filesystems make it easy to categorize and organize our data on the physical storage device.


"Sector" may refer to a physical sector or logical sector. In early days of HDDs there were only physical sectors created by dividing clusters/tracks on rotating disks into small parts. Cylinder/Head/Sector (CHS) has been a popular method of addressing before the Logical Block Addressing (LBA) was devised. Instead of directly dealing with physical sectors, OS now talks to disk controller firmware (through SATA/SCSI commands) referring an LBA number. Firmware in return maintains an LBA to CHS mapping itself, which includes ECC, G-list (disk's defect table) etc. This mapping (1:1 / sequenced / linear) (ref) is created during low-level formatting of disk drive when manufacturing, which never changes except if some sector is marked bad and remapped to some spare sector. So the OS / filesystem is aware of the physical geometry of the disk, which is propotional to the geometry of LBAs.


On flash media (SSDs, eMMC, UFS, SD cards etc.) there are no rotating disks and hence no cylinders. NAND flash is made of silicon cells, each cell consists of one (Single-Level-Cell), two (Multi-LC), three (Triple-LC) or four (Quad-LC) bits. Cells are grouped into pages (e.g. of 4KB) and pages into erase blocks (e.g. of 128 KB). LBAs to Physical Block Addresses mapping is fully controlled by Flash Translation Layer; a part of flash controller firmware. OS knows nothing about it, it can see at maximum the LBAs, not what's happening below it. Not even the ECC of failed memory cells, and that's why we don't realize the bad health of eMMC unless it fails, except by reading EXT_CSD (requires root) using mmc-utils or from /sys/class/mmc_host/*/*/life_time (if driver supports).

Since a page of memory can't be just overwritten unlike HDDs, a whole EraseBlock has to be Erased first before being Programmed (written). A side effect is that a number of pages are erased/re-written and the physical mapping changes even if a small file is edited. This unnecessary read-modify-write (RMW) is called Write Amplification. On HDDs, files aren't physically replaced unless shortened or elongated. OS is aware of these physical changes on HDD, but not on flash memory.


So after all what we are concerned with is logical sector. Storage media informs the OS of its logical sector size but “the default of 512 covers most hardware” because HDDs have been using 512B from early days, though things have changed with 4Kn format for HDDs too. 512B is the size what OS sees, in actual it's a bit larger to make some room for header, ECC etc. Physical sector size on flash storage is of no use to us.

Your queries:

I would like to know if a certain file moves on the Flash memory (internal storage), between writes/updates to it.

It depends on the definition of “move”. On flash storage, even if you don't write to a file, it may keep on changing its true physical location due to background Garbage Collection; a phenomenon controlled by FTL internally to reduce WA, to achieve Wear Leveling and to provide high write throughput (Program operations) by deleting invalid pages in background (Erase operations).

Is there some way I can get the file's location on the Flash memory (Cluster Number, Sector Number etc.)?

Yes you can get the filesystem block addresses of a file which have a linear mapping with LBAs of underlying block device (partition). But these addresses aren't the actual/physical file's location on the Flash memory. However usually one isn't concerned with true physical location unless some forensics or data recovery is involved.


~# cat /sys/block/mmcblk0/queue/logical_block_size
~# blockdev --getss /dev/block/by-name/cache
~# tune2fs -l /dev/block/by-name/cache | grep 'Block size'
Block size:               4096

So the sector size here is 512B while filesystem block size is 4KiB. Let's create a test file:

~# echo foobar >/cache/test_file
~# cat /cache/test_file
~# filefrag -sv -b512 /cache/test_file
Filesystem type is: ef53
File size of /cache/test_file is 7 (8 block of 512 bytes)
 ext:     logical_offset:        physical_offset: length:   expected: flags:   
   0:        0..       7:     307200..    307207:      8:             last,eof
/cache/test_file: 1 extent found

* debugfs -R 'stat test_file' /dev/block/by-name/cache can also be used in place of filefrag

Created file (of 7 bytes size) occupies 1 filesystem block. -b 512 converts block size (4096B) to sector size (512B). "test_file" should be at 307200th sector, same for partition and filesystem because filesystem occupies whole partition:

~# blockdev --getsize64 /dev/block/by-name/cache | awk '$1 /= 4096'
~# tune2fs -l /dev/block/by-name/cache | grep 'Block count'
Block count:              65536

Let's read the file directly from partition:

~# dd if=/dev/block/by-name/cache skip=307200 count=1 | head -c7

It's there. Now locate the file from the start of eMMC:

~# readlink /dev/block/by-name/cache
~# cat /sys/block/mmcblk0/mmcblk0p25/start
~# dd if=/dev/block/mmcblk0 skip=$(( 7471104 + 307200 )) count=1 | head -c7

So even if filesystem and partition are deleted, you can read the file (provided that it's not overwritten).

Let's do some more digging:

~# rm /cache/test_file; sync; echo -n 1 >/proc/sys/vm/drop_caches
~# dd if=/dev/block/mmcblk0 skip=$(( 7471104 + 307200 )) count=1 | head -c7

File is deleted from filesystem, but physically still there. Let's ask FTL to delete it permanently:

~# fstrim /cache; sync; echo -n 1 >/proc/sys/vm/drop_caches
~# dd if=/dev/block/mmcblk0 skip=$(( 7471104 + 307200 )) count=1 | head -c7

And it's gone. But most probably it's still there somewhere in Over-Provisioning Space, scheduled to be Erased in next GC, just we don't know where it is.


  • dd on naked partitions is a killer. Be cautious!
  • tune2fs and filefrag are part of e2fsprogs. filefrag isn't shipped with Android, build from source or try this one. fstrim is a busybox applet.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .