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Hard drives are transitioning from 512 byte to 4096 byte sector sizes, and it looks like Windows XP won't support these newer drives without additional software (such as WDalign from Western Digital)

My question is: how does this affect external hard drives? I'll be buying a 1TB USB external drive, and it'll be plugged into a mix of Windows 7 and XP machines. Is there an easy way to tell what the sector size on an external hard drive is?

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Please note that hard drive sector size != filesystem allocation unit (a.k.a "cluster") size as reported by the OS. NTFS, for example uses 4kB-sized allocation units but (on old HDDs) these are made up of 8 HDD sectors. – sigint Mar 17 '10 at 8:49
There is more information and, I think, a better answer over on Stack Overflow to the question How can i determine the sector size in windows. The suggestion there is to use the command fsutil fsinfo ntfsinfo <volume pathname> – irrational John Sep 14 '13 at 23:11
up vote 10 down vote accepted

Run wmic partition get BlockSize, StartingOffset, Name, Index from a Windows Command Prompt. The output looks like:

BlockSize  Index  Name                   StartingOffset
512        0      Disk #0, Partition #0  1048576
512        1      Disk #0, Partition #1  105906176
512        0      Disk #1, Partition #0  32256

Where block size is the drive's sector size. It unfortunately doesn't list the drive letter.

Also as I understand the article, the drive will still list that it has 512 byte sectors even though internally it uses 4kb sectors. So the only way may be to get the drive's spec sheet.

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The HDD may indeed misreport blocksize to the OS. However, if I try this on Win7 (which supports 4k sectors), it ought to report the correct blocksize. At least that way I can put a "don't use this on XP without WDAlign" sticker on the external hard drive. Any fellow commenters with 4k-sector drives, please chime in with your experiences. Thanks! – sigint Mar 18 '10 at 17:11
The reason why this actually does not work is explained in this answer over on Stack Overflow. The blocksize reported by that wmic command is apparently the logical sector size and may not agree with the physical sector size of the drive. The suggestion on SO was to use the fsutil command. – irrational John Sep 14 '13 at 23:17

I just verified this with WMIC on my windows XP box. This is the query:

C:\>wmic DISKDRIVE get bytespersector, caption  
BytesPerSector  Caption  
512             WDC WD1600AAJS-60M0A0  
4096            TrekStor HDD USB Device

The newer Toshiba external disk is reported as 4096 bytes.

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I know that you dont use linux, but just for the record:

smartctl -i /dev/...


Sector Size:      512 bytes logical/physical
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You can do this via a command prompt. Open up CMD (Windows+r then type cmd) and run chkdsk driveletter: chkdsk c: It will be listed as x bytes in each allocation unit.

alt text

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I believe this talks about the file system, not the disk itself. – Joey Mar 17 '10 at 13:58

Your physical HDD will have a physical sector size defined by manufacturer (512 or 4096 on newer storage), and then on top of that your file system creates a logical sector size.

If the two are not aligned, you will have read, modify, writes from two blocks if the data you are modifying spans two blocks.

For SSDs, altough they logically work the same way on data access, I believe their physical sectors are 1024 (due to flash memory), therefore you will need to algn the partition accordingly, Align=1024.

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This does not really address the author's question. – Ramhound Aug 29 '12 at 17:05

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