first block in ext3 filesystem

first block in ext3 filesystem

[Prashant Shah]

Hi,

I came across this

$sudo dumpe2fs /dev/sda1

4KB Block Size
Group 0: (Blocks 0-32767)
  Primary superblock at 0, Group descriptors at 1-1

1KB Block Size
Group 0: (Blocks 1-8192)
  Primary superblock at 1, Group descriptors at 2-2

Why does first block start from 0 in the 4KB block size partition and
1 in 1KB block size partition ?

Regards.

first block in ext3 filesystem

[Manish Katiyar]

On Mon, Aug 6, 2012 at 11:04 AM, Prashant Shah <pshah.mumbai@gmail.com>wrote:

> Hi,
>
> I came across this
>
> $sudo dumpe2fs /dev/sda1
>
> 4KB Block Size
> Group 0: (Blocks 0-32767)
>   Primary superblock at 0, Group descriptors at 1-1
>
> 1KB Block Size
> Group 0: (Blocks 1-8192)
>   Primary superblock at 1, Group descriptors at 2-2
>
> Why does first block start from 0 in the 4KB block size partition and
> 1 in 1KB block size partition ?
>

Let's say superblock is always written at a fixed offset of 1024 (they have
to because e2fsck has to find it) in the filesystem. What would be the
block numbers with block sizes 1k and 4k ?



>
> Regards.
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>



-- 
Thanks -
Manish
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first block in ext3 filesystem

[Prashant Shah]

Hi,

On Mon, Aug 6, 2012 at 11:49 PM, Manish Katiyar <mkatiyar@gmail.com> wrote:
> Let's say superblock is always written at a fixed offset of 1024 (they have
> to because e2fsck has to find it) in the filesystem. What would be the block
> numbers with block sizes 1k and 4k ?

I was confused about

Group 0: (Blocks 0-32767)
Group 0: (Blocks 1-8192)

One of them ends in even and other in odd number.

first block in ext3 filesystem

[Yang Chengwei]

On Mon, Aug 06, 2012 at 11:19:57AM -0700, Manish Katiyar wrote:
> 
> On Mon, Aug 6, 2012 at 11:04 AM, Prashant Shah <pshah.mumbai@gmail.com> wrote:
> 
>     Hi,
> 
>     I came across this
> 
>     $sudo dumpe2fs /dev/sda1
> 
>     4KB Block Size
>     Group 0: (Blocks 0-32767)
>       Primary superblock at 0, Group descriptors at 1-1
> 
>     1KB Block Size
>     Group 0: (Blocks 1-8192)
>       Primary superblock at 1, Group descriptors at 2-2
> 
>     Why does first block start from 0 in the 4KB block size partition and
>     1 in 1KB block size partition ?
> 
> 
> Let's say superblock is always written at a fixed offset of 1024 (they have to
As Shah said, the superblock is always written at a offset 1024. When
the block size is 4096, offset 1024 is in the first block (block 0),
while the block size is 1024, offset 1024 is in the second block (block
1).

Since group descriptor locates after superblock, so Group 0 starts from
1 when the block size is 1024 byte.

Please correct me if I'm wrong.

--
Thanks,
Chengwei

> because e2fsck has to find it) in the filesystem. What would be the block
> numbers with block sizes 1k and 4k ?
> 
>  
> 
> 
>     Regards.
> 
>     _______________________________________________
>     Kernelnewbies mailing list
>     Kernelnewbies at kernelnewbies.org
>     http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> 
> 
> 
> 
> --
> Thanks -
> Manish
> 

> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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first block in ext3 filesystem

[Mulyadi Santosa]

Hi...

On Tue, Aug 7, 2012 at 1:04 AM, Prashant Shah <pshah.mumbai@gmail.com> wrote:
> Hi,
>
> I came across this
>
> $sudo dumpe2fs /dev/sda1
>
> 4KB Block Size
> Group 0: (Blocks 0-32767)
>   Primary superblock at 0, Group descriptors at 1-1
>
> 1KB Block Size
> Group 0: (Blocks 1-8192)
>   Primary superblock at 1, Group descriptors at 2-2

I think it has something to do with the alignment. At the first case,
your 4K block size formatted partition align perfectly, so it is
usable right from block 0.

OTOH, on 1K block size, block 0 must be skipped and starting from
block 1, it align perfectly.

Not sure which alignment size your disk use. Maybe it's 4K, since
nowadays 4K disk is becoming common ones

CMIIW people...

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com