GNU bug report logs - #27884
parted reports the partition is not optimally aligned, even though it's 1MiB-aligned

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Alicia Boya García <ntrrgc <at> gmail.com>
To: bug-parted <at> gnu.org
Subject: parted reports the partition is not optimally aligned, even though
 it's 1MiB-aligned
Date: Mon, 31 Jul 2017 00:46:34 +0200

Hi.

Is there any explanation to this GNU parted output?

GNU Parted 3.2
Using /dev/sde
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) unit B                                                          
(parted) p                                                               
Model: Seagate M3 Portable (scsi)
Disk /dev/sde: 4000787029504B
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags:

Number  Start     End             Size            File system  Name  Flags
 1      1048576B  4000786153471B  4000785104896B  ext4

(parted) align-check                                                     
alignment type(min/opt)  [optimal]/minimal?                              
Partition number? 1                                                      
1 not aligned

Why does it say it's not aligned? Both the the start and the end are
1MB-aligned (and therefore trivially 4096B-aligned and 512B-aligned), am
I right?

In [1]: 1048576/4096
Out[1]: 256.0

In [2]: 4000785104896/4096
Out[2]: 976754176.0

For the record, at least it says it complies with "minimal" alignment:

(parted) align-check                                                     
alignment type(min/opt)  [optimal]/minimal? minimal                      
Partition number? 1                                                      
1 aligned

Regards,
Alicia.

Message #8 received at 27884 <at> debbugs.gnu.org (full text, mbox):

From: Phil Susi <psusi <at> ubuntu.com>
To: Alicia Boya García <ntrrgc <at> gmail.com>,
 27884 <at> debbugs.gnu.org
Subject: Re: bug#27884: parted reports the partition is not optimally aligned, 
 even though it's 1MiB-aligned
Date: Wed, 20 Sep 2017 08:55:40 -0400

On 7/30/2017 6:46 PM, Alicia Boya García wrote:
> Hi.
> 
> Is there any explanation to this GNU parted output?
> 
> GNU Parted 3.2
> Using /dev/sde
> Welcome to GNU Parted! Type 'help' to view a list of commands.
> (parted) unit B                                                          
> (parted) p                                                               
> Model: Seagate M3 Portable (scsi)
> Disk /dev/sde: 4000787029504B
> Sector size (logical/physical): 512B/4096B
> Partition Table: gpt
> Disk Flags:
> 
> Number  Start     End             Size            File system  Name  Flags
>  1      1048576B  4000786153471B  4000785104896B  ext4
> 
> (parted) align-check                                                     
> alignment type(min/opt)  [optimal]/minimal?                              
> Partition number? 1                                                      
> 1 not aligned
> 
> Why does it say it's not aligned? Both the the start and the end are
> 1MB-aligned (and therefore trivially 4096B-aligned and 512B-aligned), am
> I right?

Maybe your drive is advertising a different optimal alignment.  What
does /sys/block/sde/queue/optimal_io_size say?

Message #13 received at 27884-done <at> debbugs.gnu.org (full text, mbox):

From: Phil Susi <psusi <at> ubuntu.com>
To: Alicia Boya García <ntrrgc <at> gmail.com>,
 27884-done <at> debbugs.gnu.org
Subject: Re: bug#27884: parted reports the partition is not optimally aligned, 
 even though it's 1MiB-aligned
Date: Wed, 20 Sep 2017 10:02:49 -0400

On 9/20/2017 9:57 AM, Alicia Boya García wrote:
> Indeed.
> 
> This drive was advertising a ridiculous optimal_io_size that is not even
> a power of two (2^16-1 512-byte sectors). Unfortunately this seems to be
> the case with more Seagate drives:
> 
> http://lists.gnu.org/archive/html/bug-parted/2016-12/msg00002.html
> https://patchwork.kernel.org/patch/5249211/

You have to love drive firmware bugs, especially when the bastards never
fix them.

Message #16 received at 27884 <at> debbugs.gnu.org (full text, mbox):

From: Alicia Boya García <ntrrgc <at> gmail.com>
To: Phil Susi <psusi <at> ubuntu.com>, 27884 <at> debbugs.gnu.org
Subject: Re: bug#27884: parted reports the partition is not optimally aligned, 
 even though it's 1MiB-aligned
Date: Wed, 20 Sep 2017 15:57:05 +0200

On 09/20/2017 02:55 PM, Phil Susi wrote:
> On 7/30/2017 6:46 PM, Alicia Boya García wrote:
>> Hi.
>>
>> Is there any explanation to this GNU parted output?
>>
>> GNU Parted 3.2
>> Using /dev/sde
>> Welcome to GNU Parted! Type 'help' to view a list of commands.
>> (parted) unit B                                                          
>> (parted) p                                                               
>> Model: Seagate M3 Portable (scsi)
>> Disk /dev/sde: 4000787029504B
>> Sector size (logical/physical): 512B/4096B
>> Partition Table: gpt
>> Disk Flags:
>>
>> Number  Start     End             Size            File system  Name  Flags
>>  1      1048576B  4000786153471B  4000785104896B  ext4
>>
>> (parted) align-check                                                     
>> alignment type(min/opt)  [optimal]/minimal?                              
>> Partition number? 1                                                      
>> 1 not aligned
>>
>> Why does it say it's not aligned? Both the the start and the end are
>> 1MB-aligned (and therefore trivially 4096B-aligned and 512B-aligned), am
>> I right?
> Maybe your drive is advertising a different optimal alignment.  What
> does /sys/block/sde/queue/optimal_io_size say?
>
Indeed.

This drive was advertising a ridiculous optimal_io_size that is not even
a power of two (2^16-1 512-byte sectors). Unfortunately this seems to be
the case with more Seagate drives:

http://lists.gnu.org/archive/html/bug-parted/2016-12/msg00002.html
https://patchwork.kernel.org/patch/5249211/

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