Any advantages to having unallocated space?

Question

I am going to be setting up my hard drive soon, and one of the things I read is that many linux partitioners will give you the option to leave unallocated space between partitions. Is there any sort of advantage to doing this? If so, how large of a space should be left between partitions?

Answer 1

As far as I can see, there is little benefit from unallocated space. Partitions should be properly aligned on the disk (and that may cause some space to remain unallocated), but most GNU/Linux utilities will automatically do that.

If you're using a SSD made by Intel, you can decrease performance degradation by leaving some space unallocated at the end of the drive. It will be used for temporary storage when blocks need to be erased.

Answer 2

While there is no general advantage in leaving unallocated space between partitions, there are some cases where it may be useful - or even necessary:

• Partitions must be aligned with regard to the physical block size of the underlying device: Unaligned accesses can be measurably slower - I have seen databases being slower by as much as 30% under some workloads due to this.

  That means that you may have to leave a few KB of empty space in order for the partitions to be aligned to the 4 KiB physical sectors that are used by many modern drives.

• Disk utilities occasionally make use of empty space: One case that comes to mind is the GRUB2 bootloader, where the recommended method of installation is embedding GRUB in unallocated space before the first partition. Judging by the way bootloader sizes have grown lately, leaving a MiB or so of unallocated space before the first partition would not be unreasonable.

As for leaving unallocated space at the end of the device, it might be useful in cases where it is not possible to determine a priori how the disk space will be used. Reserving space and using Logical Volume Management (LVM) allows allocating space on demand, without cumbersome file backup/copy/move operations.