Partition X does not start on physical sector boundary.

berkov · 04-16-2013, 02:48 AM

Hi all,
I'm very new here and actually this is my first post.
The number of posts is massive so I was trying to search for the same thread before i decided to post mine, just to make sure no one has raised the same problem before. I couldn't really find anything relevant so here we go.

The story starts as usual "i've recently bought a laptop and decided to install linux on it together with Win7". 
Win7 came in first and then linux, but already on win7 installation (from so called “Windows Recovery Environment” - placed at sda1) i've chosen different than propose partition split to make my life easier when installing Ubuntu 12 later on (it think it was sda1, sda2, and big sda3). Then under Win7 I run Partition Magic (I belive it was partition magic) and cut last partition (sda3) into more to prepare for linux. Everything went ok, partition under Win7 are shown ok - no probs, no worries.
Even when i installed Ubuntu, everything was ok and actually is still ok but when i try to access the disk via gparted – the whole disc is shown as “Unallocated” space.
Cfdisk cannot access the disk either because it says that (if I remember well) partition finishes after its end – or something like this.
I tried with “fdisk –l” and here is the result:

Disk /dev/sda: 750.2 GB, 750156374016 bytes
255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0xe3102a4b

Device Boot Start End Blocks Id System
/dev/sda1 2048 52430847 26214400 c W95 FAT32 (LBA)
/dev/sda2 * 52430848 262164734 104866943+ 7 HPFS/NTFS/exFAT
/dev/sda3 262164798 1057060934 397448068+ 7 HPFS/NTFS/exFAT
Partition 3 does not start on physical sector boundary.
/dev/sda4 1057060935 1465160129 204049597+ f W95 Ext'd (LBA)
Partition 4 does not start on physical sector boundary.
/dev/sda5 1057060998 1415005199 178972101 7 HPFS/NTFS/exFAT
Partition 5 does not start on physical sector boundary.
/dev/sda6 1415006208 1431021551 8007672 82 Linux swap / Solaris
/dev/sda7 1431023616 1465147391 17061888 83 Linux

Does anyone know what the problem is?
I would like to be able to change the partition tables under linux at some point so would be nice to make Linux see the disk correctly.
On top of this, I’ve read some posts on internet that this might have some minor impact on the disk performance which is also not so good news to me.
I should also probably add here that all Linux distros see the disk with this error. I’ve tried Live CD and I’m having exactly the same problem.

Any idea why?
And the most important how to SAFELY fix it?

Will be grateful for any hint.

Thanks
berkov

TobiSGD · 04-16-2013, 08:05 AM

The physical sector size of this disk is 4096 bytes, but the logical sector size is 512 bytes. To get rid of the warnings (and the performance impacts) you have to align those values, which means that the start sector of a partition should be a multiple of 8 (4096/512). If you repartition the disk with this in mind the warnings will disappear.

chrism01 · 04-16-2013, 08:10 AM

It also looks like you've skipped putting an Extended partition on.
Basically, a disk can have 4 Primary partitions, or 3 Primary, plus and Extended one, that you can then create Logical partitions inside of.
See
http://www.tldp.org/HOWTO/Partition/...ion-types.html
https://en.wikipedia.org/wiki/Disk_partitioning

berkov · 04-16-2013, 08:30 AM

@TobiSGD - thanks, but why multiple of 8 and why not multiple of 4096 if the physical sector is 4096? Another question is if there is any command or script/program that could safely move a bit all partitions for few bytes so i don't have to reformat everything? that would be very painful.

@chrism01, thanks too!, i've also noticed that but it was partition magic and i thought that this rules might be somehow a legacy thing now. i would have thought that without extended partition the partition table won;t be understood by any OS, but it clearly means that it is ok, dont really get it. Is it important then or not?

TobiSGD · 04-16-2013, 10:36 AM

Quote:

Originally Posted by berkov

@TobiSGD - thanks, but why multiple of 8 and why not multiple of 4096 if the physical sector is 4096?

Because fdisk uses logical sectors as unit, so 8 sectors that fdisk shows you are 1 physical sector.

Quote:

Another question is if there is any command or script/program that could safely move a bit all partitions for few bytes so i don't have to reformat everything?

You would have to shrink the filesystem, move the partitions around and then fit the filesystem again to the partition size. None of those operations can be called safe and you should have to take a backup before doing that anyways. Since I assume that you already have a recent backup (as you should have) it would be easier and faster to just repartition the disk and restore the backup.

berkov · 04-17-2013, 08:46 AM

hi TobiSGD

thanks a lot for the answer...
i guess i will have to wait for some next "random system crash" and only then use that opportunity to do repartitioning. coz with 2 OSs and 750gb this activity would take 1-2 days and there is no big "value added" of doing it now.

thanks again!