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Stayvoid 08-30-2012 02:24 PM

How to align partitions?
 
Hi,

I'd like to know how to create aligned partitions on a 160GB disk
which uses a 512B sector size.
(Partition table: msdos)

I've got the theory [1, 2], but I can't make it work.

I'd like to have three partitions:
1. ext3 ~ 100mb /boot
2. linux-swap ~ 1GB swap
3. ext3 (for the rest of the system)

How to adjust the sizes?

I'm planning to encrypt swap and the third partition with dm-crypt (not LUKS).
Separate /boot is needed to mount and decrypt them after booting.

[1] http://forums.gentoo.org/viewtopic-t-838522.html
[2] http://superuser.com/questions/349887/gnu-parted-how-to-deal-with-the-error-about-proper-aligment-of-partitions

Thanks

Sébastien Luttringer 08-30-2012 03:17 PM

How to align partitions?
 
On Thu, Aug 30, 2012 at 4:24 PM, Stayvoid <stayvoid@gmail.com> wrote:
> Hi,
>
> I'd like to know how to create aligned partitions on a 160GB disk
> which uses a 512B sector size.

Almost all recent HDD/SSD have 4KiB internal sector (even when
reported as 512B by ATA). Read [1].

> (Partition table: msdos)
>
> I've got the theory [1, 2], but I can't make it work.
>
> I'd like to have three partitions:
> 1. ext3 ~ 100mb /boot
> 2. linux-swap ~ 1GB swap
> 3. ext3 (for the rest of the system)
>
> How to adjust the sizes?
Recent versions of fdiks, parted, gdisk do it for you. This is boring
in some cases.

[1] https://ata.wiki.kernel.org/index.php/ATA_4_KiB_sector_issues

--
Sébastien "Seblu" Luttringer
www.seblu.net

Stayvoid 08-30-2012 09:45 PM

How to align partitions?
 
> Recent versions of fdiks, parted, gdisk do it for you.

I use parted.
AFAICT it can tell that partitions aren't aligned, but there is no
option to do it automatically.

Could you help me to do the math? All these bytes give me a headache.

Thanks

Paul Gideon Dann 09-03-2012 09:40 AM

How to align partitions?
 
On Friday 31 Aug 2012 01:45:40 Stayvoid wrote:
> > Recent versions of fdiks, parted, gdisk do it for you.
>
> I use parted.
> AFAICT it can tell that partitions aren't aligned, but there is no
> option to do it automatically.
>
> Could you help me to do the math? All these bytes give me a headache.
>
> Thanks

This is what I do:

In parted, enter "unit b" to switch to bytes, because then you know what
you're working with.

I like to start my first partition at 1048576, which is 1Mb into the disk, and
end it at 104857599, which makes it 99Mb long. After that, I use a single
partition spanning the rest of the disk, starting at 104857600 (100Mb), and
ending at a multiple of (1024*1024=1048576). I use LMV or RAID+LVM on top of
that.

Don't forget that the end point for each partition will be one byte before a
Mb marker, so my first partition, ending at 104857599, is 1b before the 99Mb
mark. The size of the partition includes this end byte, so the partition is a
full 99Mb's worth of bytes.

I hope this helps,
Paul

C Anthony Risinger 09-04-2012 04:19 AM

How to align partitions?
 
On Sep 3, 2012 4:41 PM, "Paul Gideon Dann" <pdgiddie@gmail.com> wrote:
>
> On Friday 31 Aug 2012 01:45:40 Stayvoid wrote:
> > > Recent versions of fdiks, parted, gdisk do it for you.
> >
> > I use parted.
> > AFAICT it can tell that partitions aren't aligned, but there is no
> > option to do it automatically.
> >
> > Could you help me to do the math? All these bytes give me a headache.
> >
> > Thanks
>
> This is what I do:
>
> In parted, enter "unit b" to switch to bytes, because then you know what
> you're working with.
>
> I like to start my first partition at 1048576, which is 1Mb into the
disk, and
> end it at 104857599, which makes it 99Mb long. After that, I use a single
> partition spanning the rest of the disk, starting at 104857600 (100Mb),
and
> ending at a multiple of (1024*1024=1048576). I use LMV or RAID+LVM on
top of
> that.
>
> Don't forget that the end point for each partition will be one byte
before a
> Mb marker, so my first partition, ending at 104857599, is 1b before the
99Mb
> mark. The size of the partition includes this end byte, so the partition
is a
> full 99Mb's worth of bytes.

Yuk! :-) I'd only change the unit setting:

u mib

... much simpler than bytes, and then +1 and -1 are always aligned (and
appropriate for MBR)

I simply leave ~1mib gap between partitions ... something like:

mkpart pri ... 1 129
mkpart pri ... 130 1154
mkpart pri ... 1155 -1

... seems to work universally.

--

C Anthony

C Anthony Risinger 09-04-2012 04:34 AM

How to align partitions?
 
On Mon, Sep 3, 2012 at 11:19 PM, C Anthony Risinger <anthony@xtfx.me> wrote:
>
> Yuk! :-) I'd only change the unit setting:
>
> u mib
>
> ... much simpler than bytes, and then +1 and -1 are always aligned (and
> appropriate for MBR)
>
> I simply leave ~1mib gap between partitions ... something like:
>
> mkpart pri ... 1 129
> mkpart pri ... 130 1154
> mkpart pri ... 1155 -1
>
> ... seems to work universally.

er, my mistake ... i *used* to leave a 1MiB gap, but as long as the
default unit is MiB, and you specify offsets using simple integers,
parted will automatically start/end on the correct byte:

(parted) u mib
(parted) mkpart pri 1 129
(parted) mkpart pri 129 641
(parted) p
[...]
Number Start End Size File system Name Flags
1 1.00MiB 129MiB 128MiB
2 129MiB 641MiB 512MiB

(parted) u b
(parted) p
Number Start End Size File system Name Flags
1 1048576B 135266303B 134217728B
2 135266304B 672137215B 536870912B

--

C Anthony

Nicolas Sebrecht 09-04-2012 07:01 AM

How to align partitions?
 
The 03/09/12, Paul Gideon Dann wrote:

> I like to start my first partition at 1048576, which is 1Mb into the disk, and
> end it at 104857599, which makes it 99Mb long. After that, I use a single
> partition spanning the rest of the disk, starting at 104857600 (100Mb), and
> ending at a multiple of (1024*1024=1048576). I use LMV or RAID+LVM on top of
> that.

LVM needs dedicated configuration, too.
AFAIK, some RAID can't be aligned at all due to metadata.

A good article is from Theodore Ts'o:

http://tytso.livejournal.com/2009/02/20/

--
Nicolas Sebrecht

Paul Gideon Dann 09-04-2012 09:27 AM

How to align partitions?
 
On Monday 03 Sep 2012 23:34:34 C Anthony Risinger wrote:
> On Mon, Sep 3, 2012 at 11:19 PM, C Anthony Risinger <anthony@xtfx.me> wrote:
> > Yuk! :-) I'd only change the unit setting:
> >
> > u mib
> >
> > ... much simpler than bytes, and then +1 and -1 are always aligned (and
> > appropriate for MBR)
> >
> > I simply leave ~1mib gap between partitions ... something like:
> >
> > mkpart pri ... 1 129
> > mkpart pri ... 130 1154
> > mkpart pri ... 1155 -1
> >
> > ... seems to work universally.
>
> er, my mistake ... i *used* to leave a 1MiB gap, but as long as the
> default unit is MiB, and you specify offsets using simple integers,
> parted will automatically start/end on the correct byte:
>
> (parted) u mib
> (parted) mkpart pri 1 129
> (parted) mkpart pri 129 641
> (parted) p
> [...]
> Number Start End Size File system Name Flags
> 1 1.00MiB 129MiB 128MiB
> 2 129MiB 641MiB 512MiB
>
> (parted) u b
> (parted) p
> Number Start End Size File system Name Flags
> 1 1048576B 135266303B 134217728B
> 2 135266304B 672137215B 536870912B

Thanks, excellent tip. I wasn't aware of the mib option.

Paul

Stayvoid 09-04-2012 07:55 PM

How to align partitions?
 
> Could you help me to do the math? All these bytes give me a headache.

I used fdisk.
Looks like that it automatically aligns everything.
Could anyone confirm this?

Cheers


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