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Date:	Mon, 30 Apr 2012 13:37:42 -0400
From:	Jeff Moyer <>
To:	Eric Sandeen <>
Cc:	Daniel Drake <>,
Subject: Re: Determining if an ext4 fs uses the whole partition

Eric Sandeen <> writes:

> On 4/30/12 12:19 PM, Daniel Drake wrote:
>> Hi,
>> OLPC has started using ext4 online resizing to grow our filesystems to
>> use the whole SD card on first boot - something we never did before.
>> Working very nicely, thanks!
>> I'm trying to simplify/improve the scripts involved in doing this.
>> How can I programatically check if an ext4 fs already fills its
>> partition, or if it has room to grow?
>> The numbers produced by dumpe2fs (e.g. block count) or "df" don't seem
>> to exactly line up with the sizes produced by fdisk.
> Do you have an example of this?
> For starters, use fdisk -u to get 512-byte sector units,
> otherwise it's just inscrutable CHS magic.

Note that fdisk -u gives sector units, which may or may not be 512

$ sudo fdisk -lu /dev/sdb
Note: sector size is 4096 (not 512)

Disk /dev/sdb: 300.1 GB, 300069052416 bytes
255 heads, 63 sectors/track, 4560 cylinders, total 73259046 sectors
Units = sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

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