6

I am wondering what Start and End value to choose when partitioning my ext. SSD using fdisk.

fdisk suggests 2048-250069679, default 2048 but 250069679 cannot be divided by 512 nor by 2048. Wouldn't it be better to set the Start and End value to a number that can be divided by 512 or 2048 or 4096?

For example: Start 4096 and End 250068992

Command (m for help): p

Disk /dev/sda: 119,2 GiB, 128035676160 bytes, 250069680 sectors
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: 0xa4b57300


Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-250069679, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-250069679, default 250069679): 

Created a new partition 1 of type 'Linux' and of size 119,2 GiB.


Command (m for help): p
Disk /dev/sda: 119,2 GiB, 128035676160 bytes, 250069680 sectors
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: 0xa4b57300

Device     Boot Start       End   Sectors   Size Id Type
/dev/sda1        2048 250069679 250067632 119,2G 83 Linux

Command (m for help): i
Selected partition 1
         Device: /dev/sda1
          Start: 2048
            End: 250069679
        Sectors: 250067632
      Cylinders: 15566
           Size: 119,2G
             Id: 83
           Type: Linux
    Start-C/H/S: 0/32/33
      End-C/H/S: 206/29/63


mkfs.ext4 /dev/sda1
mke2fs 1.43.4 (31-Jan-2017)
Ein Dateisystems mit 31258454 (4k) Blöcken und 7815168 Inodes wird erzeugt.
UUID des Dateisystems: fdce9286-4545-447c-9cca-7d67f5bb9f43
Superblock-Sicherungskopien gespeichert in den Blöcken: 
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
    4096000, 7962624, 11239424, 20480000, 23887872


fdisk -l
Disk /dev/sda: 119,2 GiB, 128035676160 bytes, 250069680 sectors
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: 0xa4b57300

Device     Boot Start       End   Sectors   Size Id Type
/dev/sda1        2048 250069679 250067632 119,2G 83 Linux

And how can it be that the Sectors number is lower than the End value?

Command (m for help): i
Selected partition 1
         Device: /dev/sda1
          Start: 2048
            End: 250069679
        Sectors: 250067632
      Cylinders: 15566
           Size: 119,2G
             Id: 83
           Type: Linux
    Start-C/H/S: 0/32/33
      End-C/H/S: 206/29/63

  • Sectors is End minus Start. Usually for alignment, only Start matters. – frostschutz Apr 6 at 8:59
  • have you considered using a higher level (therefore easier to use) tool, such as gparted? – ctrl-alt-delor Apr 6 at 10:34
  • @ctrl-alt-delor normaly i use gparted, but this time i have no gui installed. – AlexOnLinux Apr 6 at 12:01
  • Live OS (boot off of USB, use ssh -X and run it remotely, or parted. – ctrl-alt-delor Apr 6 at 14:58
  • @ctrl-alt-delor first: it's a raspberry pi using raspbian lite without gui. second: whats the problem of understanding how to properly align third: did i use the tools fdisk and mkfs.ext4 incorrect? – AlexOnLinux Apr 7 at 6:37
5

Alignment doesn’t matter for the end sector. Sectors are numbered from 0; fdisk is suggesting the last sector on your disk (which has 250069680 sectors).

  Start: 2048
    End: 250069679
Sectors: 250067632

is correct, 250069679 minus 2048 plus one is 250067632: the partition contains 250067632 sectors, starting at offset 2048.

  • i am wondering why the end-value is not important. do you know why perhaps? – AlexOnLinux Apr 6 at 12:01
  • @AlexOnLinux your choices are either to use all the sectors available or not. If you want them all and the disk has a size which is not a multiple of 512/2048/4096 then the end will not be aligned. – icarus Apr 6 at 17:35
  • @icarus Having the Start and End aligned gives any performance advantages? Is it usefull to properly align the End-value when using multiple partitions? – AlexOnLinux Apr 7 at 6:41
  • @AlexOnLinux all partitions should have their start aligned for performance (and wear-and-tear on SSDs, although that’s less of an issue than people make it out to be). If you create partitions with GPT and no space between them, the end of each partition will be aligned, apart from the last one in some cases (as in your situation). – Stephen Kitt Apr 7 at 6:56
  • Miss alignment, of the start, will affect the whole partition, but of the end only affects the end and the next partition. – ctrl-alt-delor Apr 7 at 9:44

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