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[solved] 4k disk alignment confusion
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Vrenn
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Joined: 15 Dec 2004
Posts: 195

PostPosted: Thu Jul 03, 2014 5:43 pm    Post subject: [solved] 4k disk alignment confusion Reply with quote

Dear Gentoo Experts. When I was setting up my laptop I probably made some mistakes.

The first is my too small boot-partition, I know.
On the 4k-alignment I thought it was matching:
Code:
Disk /dev/sda: 698,7 GiB, 750156374016 bytes, 1465149168 sectors
Units: Sektoren of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x8307eef8
Partition 1 does not start on physical sector boundary.

Gerät     Boot     Start       Ende    Blocks  Id System
/dev/sda1             63      80324     40131  de Dell Utility
/dev/sda2 *        81920   20496383  10207232   7 HPFS/NTFS/exFAT
/dev/sda3       20496384  750415871 364959744   7 HPFS/NTFS/exFAT
/dev/sda4      750415872 1465149167 357366648   5 Extended
/dev/sda5 *    750417920  750483455     32768  83 Linux
/dev/sda6      750485504  767483903   8499200  82 Linux swap / Solaris
/dev/sda7      767485952 1465149167 348831608  83 Linux
using Dell Partition(1), recover(2) windows7(3) and Gentoo in the extended.
Then I was reading that the Partition offset on an 4k drive has to be divided by 4096 without comma.
sda7 is 767485952 / 4096 = 187 374,5 leaving ,5!
As ext4 uses 4096 too that partition seems to have a bad alinment.
http://wiki.hetzner.de has an example for correct alignment:
Code:
/dev/sda3         5244928  1465149167   729952120   fd  Linux raid autodetect

5244928 / 4096 = 1 280,5. another 0.5!
Can you help me please where is the error: on my disk or in my brain?
I am not only using Gentoo for "full speed", rather for full understanding!
parted /dev/sda align-check opt 7 tells me "7 aligned". but aligned on logical 512 or physical 4096?
Do I need to kill my boot (sda5, for being so dump sparing on the wrong place), or my root to?
I want to do it right.

Thank you for any help.
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With nice greetings
Vrenn


Last edited by Vrenn on Thu Jul 03, 2014 7:10 pm; edited 1 time in total
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ulenrich
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Joined: 10 Oct 2010
Posts: 1131

PostPosted: Thu Jul 03, 2014 7:00 pm    Post subject: Reply with quote

Code:
~$ echo "767485952 * 512 / 4096"|bc -l
95935744.00000000000000000000

seems ok
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Vrenn
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PostPosted: Thu Jul 03, 2014 7:10 pm    Post subject: Reply with quote

" * 512" forgot fdisk tells me sectors, found error: my brain.
Thank you!
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Vrenn
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