I read an article on aligning file-systems on partitions and this said that:
When manipulating MBR disks, be aware that the alignment of extended partitions is unimportant. These partitions hold one-sector data structures that define logical partitions, so in a real sense, extended partitions can't be properly aligned.
Could someone explain in more detail why alignment of extended partitions is unimportant?
Alignment is important on partitions containing data, in order to maximise the chance that block operations will match whatever the underlying block structure is (4K on modern hard drives, more than that on flash-based drives).
Extended partitions don't contain data, they're simply containers for logical partitions. The only operation which is done on extended partitions is reading the single 512-byte sector which defines the logical partitions, and writing it when modifying the logical partition structure (so hardly ever). Because that operation only involves a single sector, it can never match a larger block size, so any writes will be sub-optimal and there's no way of improving that. The alignment of the extended partition itself doesn't affect the possible alignment of the logical partitions it contains, so there's no need to align it there either.
Modern disks have tracks of varying length (near the border tracks are longer). They also cache data extensively (they have quite capable CPUS and memory, some hacker even installed a Linux system on one). They also remap bad blocks (inevitable given the data density) transparently to spare blocks.
As a result, data alignment issues that used to be critical in days of yore are mostly irrelevant today. And the data useful to really tune for performance just isn't available to anybody.
