[clug] 3TB (4k sector) disk question

Michael James michael at james.st
Sun Sep 2 03:17:11 MDT 2012

On 01/09/2012, at 6:49 PM, Eyal Lebedinsky wrote:

> Today I bought a 3TB disk, which originally was in a USB3 case (now out of it).
> When introduced linux (as bare SATA) it seems that a sector size of 512B is used,
> and the disk size is limited.
> 'hdparm -I' knows that this is a native 4k disk:
> 	Model Number:       ST3000DM001-9YN166
> 	Logical  Sector size:                   512 bytes
> 	Physical Sector size:                  4096 bytes	
> 	Logical Sector-0 offset:                  0 bytes	
> 	device size with M = 1024*1024:     2861588 MBytes
> 	device size with M = 1000*1000:     3000592 MBytes (3000 GB)
> However parted thinks otherwise (I created one large GPT partition):
> # parted /dev/sdi
> GNU Parted 3.0
> Using /dev/sdi
> Welcome to GNU Parted! Type 'help' to view a list of commands.
> (parted) print
> Model: ATA ST3000DM001-9YN1 (scsi)
> Disk /dev/sdi: 2199GB
> Sector size (logical/physical): 512B/512B
> Partition Table: gpt
> Number  Start   End     Size    File system  Name     Flags
> 1      1049kB  2199GB  2199GB  ext2         primary
> Note the line 'Sector size (logical/physical): 512B/512B'.
> How do I make linux use 4k sector size? Or is there a jumper
> on the disk? Or a special SATA command to configure the disk?
> Also, should GPT not be able to create very large disks even with 512B
> sectors, using the 64bit internal pointers/sizes/etc.? Where is the
> disk size limit coming from?

Dear Eyal,

If you knew enough to partition it GPT you probably know this
 but I hope it's worth putting put for the list.

The 2 TB limit is inherent in Master Boot Record (MBR/MSDOS) partitioning.
The field that delimits a partition doesn't have enough bits to describe anything bigger.

Either it's not done in terms of logical blocks or you can't change that anyway.

Modern disks actually work in 4 KB blocks, but present logically as 512 Byte blocks.
If you partition a disk NOT on 4 KB boundaries; expect 10 x less performance.

This is explained quite well here:  http://www.rodsbooks.com/gdisk/

BTW Rod's gdisk partitioning tool is quite a groovy little utility.
Acts like fdisk, writes GPT partition tables.


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