To elaborate on when it's required, to the best of my knowledge, three technologies require attention to alignment:
- Advanced Format hard disks -- those that use 4096-byte physical sectors but that report a 512-byte sector size to the OS
- Some (but not all) types of RAID configuration
If you don't use any of these technologies, you don't need to worry about alignment. If your partitions are aligned as described below, you'll lose a tiny amount of disk space, but nothing worse will happen.
Details of the minimum alignment values vary between these technologies, as do the precise effects of misalignment. (I wrote an article on Advanced Format disks
for IBM developerWorks a while back, with some simple benchmark tests on an early AF disk.) To the best of my knowledge, though, aligning on 1 MiB (2048-sector) boundaries produces correct alignment with all of these technologies. Most partitioning tools released in the last year or so align on 1 MiB boundaries by default, so you're pretty safe with modern tools. FWIW, Microsoft switched to 1 MiB alignment with Windows Vista, but Linux tools lagged behind on this change. If you're using something older than a year or two, there's a chance that it aligns on cylinder boundaries. Such alignment was beneficial 20 or more years ago, but has been pointless for at least the past decade, and will likely degrade performance if you use AF disks, some types of RAID, or SSDs.
As PiElle says, recent versions of Anaconda have aligned properly (on 1 MiB boundaries). I'm not sure which version of Fedora was the first to have an Anaconda that aligns on 1 MiB boundaries, though.
If there's any doubt in your mind, the best approach is to check the alignment. You can do this with parted, but you've got to tell it to report values in sectors, via "unit s", as in:
# parted /dev/sdb unit s print
Model: ATA MAXTOR STM332062 (scsi)
Disk /dev/sdb: 625142448s
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Number Start End Size File system Name Flags
1 2048s 514047s 512000s fat32 EFI System boot, hidden
2 514048s 923647s 409600s ext2 Spare /boot
3 923648s 625142414s 624218767s Linux LVM lvm
This example shows start sector numbers of 2048, 514,048, and 923,648. These values are all multiples of 2048, meaning that the partitions are all properly aligned. In some cases, alignment on smaller values is fine; on an Advanced Format disk, if the start sectors are multiples of 8, all is fine.
Even if a partition is not
aligned on a suitable multiple, it might not be a problem. Extended partitions on MBR disks need not be so aligned, for instance -- it's mainly filesystem data structures that need to be aligned, and they're stored in primary partitions, logical partitions, or logical volumes, not in extended partitions. BIOS Boot Partitions on GPT disks also don't need to be aligned. (In theory, they do suffer performance degradation, but probably only on writing. BIOS Boot Partitions are so small and are written so seldom that improper alignment has no effect on day-to-day use of the computer.)