Question about alignment on WD drives

[eli2k]

On the newer 4K format WD drives, when used in the XP environment, the drive must be 'aligned' to function properly. If I align the drive for use under XP, and later use the drive under Win7, does the drive need to be reformatted and realigned to function well, or can I just use it normally? Thanks.

 

[Anteaus]

Yes. Personally I'd avoid using them until you can properly support GPT. The whole realignment thing was done just to sell the drives to XP users, but they weren't really designed for that. It's a bandaid. Not saying you'd have problems though. That's up to you to find out.

 

[eli2k]

Hmm, I guess I can return it. It seems all the new drives now are "advanced format," like the new WD20EURS...

 

[murphyc]

If I align the drive for use under XP, and later use the drive under Win7, does the drive need to be reformatted and realigned to function well, or can I just use it normally?

No. Windows Vista and 7 will partition any disk "aligned" on 4KB sector boundaries. XP predates 4K sectors so it doesn't do this. The XP alignment tools merely partition the disk aligned on 4K sectors, because the included XP tools won't do that.

The alignment is just about the starting LBA of each partition on the disk, information written into the MBR on the disk. When you move this to Windows 7, it reads the MBR and sees the same starting LBA for your partitions as XP did.

 

[murphyc]

Yes. Personally I'd avoid using them until you can properly support GPT. The whole realignment thing was done just to sell the drives to XP users, but they weren't really designed for that. It's a bandaid. Not saying you'd have problems though. That's up to you to find out.

I don't understand this answer.

 

[mv2devnull]

The whole realignment thing was done just to sell the drives to XP users, but they weren't really designed for that. It's a bandaid.

You seem to be referring to the offset feature that some early 4K 512e drives had. With a jumper one could activate the offset mode. In that mode the drive adds an offset (probably +1) to every LBA. Thus, when OS/BIOS refers to LBA 0 (the MBR), the disk returns physical LBA 1, when reading LBA 63 the disk returns physical LBA 64, ...

That only aligns the first partition, when the partition is set to start from LBA 63 (like XP's fdisk does). One partition is typical for default Windows installation, so "everybody" seems happy with that kludge workaround.


The cleaner solution is to partition the drive with a tool that does the Right Thing. Once the partitions are properly aligned, they are properly aligned for every OS that uses those partitions. An install of Windows Y over Windows X preferably overwrites the system volume, but it does not need to adjust partition table.

 

[murphyc]

@mv2devnull

Since LBA is a logical block address there isn't a physical logical block address. 🙂 It's just an LBA offset, but it works exactly as you described.

The desired result with most any file system using 4K allocation blocks, is a filesystem allocation block directly corresponds to the underlying 4K physical sector (despite requiring eight 512 byte LBA's to describe this relationship).

The jumper offset is for single partition disks only, and should only be used with the XP partitioning tool (or older tools that start the first partition at LBA 63).

And I also prefer not depending on jumpers. A modern tool will use a starting sector of 2048, leaving a lot more padding between the MBR and the first partition. Not terribly important but can be useful if the disk is repurposed for Linux since that MBR gap is used for one of the bootloader stages.