I run a dual-boot (windows XP on ntfs + ubuntu 10.04 on ext3) on a crappy 6 year old laptop. Today I wanted to shread 8gb or so off the right end of my XP partition and give it to ubuntu. I ended up getting an "unable to satisfy all constraints" error when trying to enlarge the extended partition ubuntu was sitting on, which I suppose was because it had problems "rounding" to the nearest MiB. A google search into some forum post (which I can't find anymore) said you could just tell it to do no alignment (the choices were MiB, Cylinder, or None). I did this and everything seemed to work fine.

I just rebooted and it hung after selecting Ubuntu from the GRUB loader. However, when I restarted it again (mostly absent-mindedly) it suddenly worked (this itself is weird - I was expecting having to manually change GRUB, as GParted itself suggested during the partitioning), though some things seemed sluggish for a few minutes (I can't tell anymore).

Feeling paranoid about the weird hanging, auto-solution, and sluggishness, I did some more googling. I turns out that the GParted document says: "Use None only if you have an in-depth knowledge of disk structure, partition tables, and boot records. This setting places partition boundaries relative to the end of any immediately preceding partition on the disk device. This setting is not guaranteed to reserve or respect space required for boot records." Further reading/googling seems to say that I also may be missing out on extra performance on SSDs or compatibility with old OSs, though neither of these apply to me.

So, questions:

"Considering I do not have the "in-depth knowledge" suggested by the GParted docs, will I be fine? Should I expect weird problems to crop up in the future? If so, what is the fastest way for me to realign (I'm guessing GParted, but maybe someone else knows a few tricks)?"

Thank you, -Yan


If your laptop 6 years old, I would expect its hard drive to use 512-byte sectors (i.e. 1 physical sector = 1 virtual sector). In this case any alignment is a good alignment - the whole point of the alignment is to ensure that filesystem clusters are aligned with physical sectors - any misalignment is only possible if physical sector size is larger than 512 bytes.

I'm not sure how any misalignment can cause intermittent boot errors you're describing - either it boots or it's not :)

  • So in the future, if I had a more modern laptop, are you saying it would be different because the physical = virtual sector would be different? I was worried about sluggishness because of things like this: rodsbooks.com/gdisk/advice.html , and I suspect this was what you were talking about (I guess 1 virtual sector = 8 physical sectors in this case)? The boot stuff was kind of spooky but seems okay since at least it boots =/ – Yan X Zhang Oct 31 '11 at 1:44
  • Yes, partition alignment is only relevant to modern (post-2009) large HDDs and to SSDs. So it may be an issue one a new laptop – Sergey Oct 31 '11 at 2:12

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