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I am familiar with what partitions are, but I saw a question about aligned partitions on Ask Ubuntu, and realised I didn't know what "aligned partitions" are.

So what does it mean to "align" partitions? What are the benefits, and the downsides?

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3 Answers 3

Aligning the partition means to align it to match the true, underlying block structure.

For a long time now hard disks have used 512 byte blocks. Because this has gone on for a long time it is now almost impossible to change the block size. Too much software would need to be fixed.

On an SSD the true block size could be 128 KB. On a RAID array it might be 64 KB. On an advanced format drive it will be 4 KB.

For backward compatibility the drive continues to work with 512 byte blocks. But for performance reasons your system really should know the true block size.

On of the easiest performance tweaks to make is to align the drive partition with the true block size so that when your OS does write 4 KB or 64 KB or 128 KB it writes a full block.

If the partition was not aligned then the result would be to write 512 bytes to the first block and 4K - 512 bytes to the second block, forcing the disk/SSD/RAID to do two read-modify-write cycles instead of one write.

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Dunno if this is helpful, but my understanding was that partition alignment is when you align a given partition with an underlying RAID stripe units.

Apparently, performance may suck when you use a hardware-based RAID or software-based; problems could arise if the starting location of the partition is not aligned with a stripe unit boundary in the disk partition that is created on the RAID.

Depending on the factoring for creating volume clusters, a volume cluster may be created over a stripe unit boundary instead of next to the stripe unit boundary. This behavior could cause a misaligned partition.

I may be way off and this could have nothing to do with RAID ;)

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