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After shrinking a read only filesystem with resize2fs on GNU/Linux, how do i determine the correct partition entry for the shrunken filesystem?

Initial partition scheme of remote host:

Disk /dev/sda: 1,8 TiB, 1999844147200 bytes, 3905945600 sectors
Disk model: xxx       
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xf79ea8df

Device     Boot      Start        End    Sectors  Size Id Type
/dev/sda1  *          2048     487423     485376  237M 83 Linux
/dev/sda2           487424 3841943551 3841456128  1,8T 83 Linux
/dev/sda3       3841943552 3883886591   41943040   20G 83 Linux


Command (m for help):

Issuing resize command:

[root@home ~]# resize2fs /dev/sda2 200G
resize2fs 1.44.5 (15-Dec-2018)
Resizing the filesystem on /dev/sda2 to 52428800 (4k) blocks.
The filesystem on /dev/sda2 is now 52428800 (4k) blocks long.

When recreating the partition entry for /dev/sda2 with 487424 as start sector, and a size of 8 times 52428800 * 512 bytes blocks, does the created partition really cover the whole shrunken filesystem and how can that be proven ?

Disk /dev/sda: 1,8 TiB, 1999844147200 bytes, 3905945600 sectors
Disk model: xxx       
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xf79ea8df

Device     Boot      Start        End   Sectors  Size Id Type
/dev/sda1  *          2048     487423    485376  237M 83 Linux
/dev/sda2           487424  419917824 419430401  200G 83 Linux
/dev/sda3       3841943552 3883886591  41943040   20G 83 Linux


Command (m for help):
Torsten
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    Empirically, the size of a partition seems to be equal to or greater than "Block count" * "Block size" as reported by dumpe2fs -h. This is also the method used in the answer to this other question (you may even flag your question as a duplicate of that one if you feel yours is answered). Though I couldn't find any reference for the assertion that "Block count" represents the total size of the file system. – fra-san Oct 29 '20 at 16:30
  • I thought of recognizing the last block of the filesystem on the last block covered by the partition as a way to be sure it fits - but how do i recognize the last block ? – Torsten Oct 29 '20 at 16:36
  • Unfortunately, the other question does not have any answers providing information about how to calculate an related correct partition entry. Are there any alignment issues ? Does a partition entry provide some extra space for filesystem meta data ? Or is the correct partition size always exactly the filesystem size, regardless of alignment and other unknown factors? – Torsten Oct 29 '20 at 16:43

0 Answers0