[DragonFlyBSD - Bug #2830] gpt(8) doesn't align partitions to 1MB blocks

bugtracker-admin at leaf.dragonflybsd.org bugtracker-admin at leaf.dragonflybsd.org
Mon Dec 28 06:05:09 PST 2015

Issue #2830 has been updated by pascii.

File 0001-Align-partitions-to-1MiB.patch added

Hi!. Here's a fix. It will align new slices to 2k sectors. If you don't specify a starting sector in gpt add, it will align the slice. If you do specify it, nothing different will happen. It also works for gpt boot, which does not demand a specific starting sector.

Bug #2830: gpt(8) doesn't align partitions to 1MB blocks

* Author: ftigeot
* Status: New
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
The GPT partition scheme management utility, gpt(8) doesn't manage partition alignment at all.

# gpt create /dev/da1
# gpt boot /dev/da1
# gpt show /dev/da1
      start       size  index  contents
          0          1      -  PMBR
          1          1      -  Pri GPT header
          2         32      -  Pri GPT table
         34    2097152      0  GPT part - DragonFly Label32

We can see the just created boot partition starts on the legacy sector 34 offset, 17KB from the start of the device.

This isn't divisible by the physical sector size of modern disk devices (4KB).
It isn't optimal with SSD either: they typically use 8KB or bigger erase blocks.

gpt(8) should behave in the same as disklabel64 and align partitions to 1MB boundaries.

0001-Align-partitions-to-1MiB.patch (1.86 KB)

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