Benefits of multiple partitions

Benefits of multiple partitions

Logical partitions require extended partitions. In Windows, extended partitions can be used to create many logical partitions.

Creating more than one partition has the following advantages:

• Separation of the operating system (OS) and program files from user files. This allows image backups (or clones) to be made of only the operating system and installed software.
• Having a separate area for operating system virtual memory swapping/paging.
• Keeping frequently used programs and data near each other.
• Having cache and log files separate from other files. These can change size dynamically and rapidly, potentially making a file system full.
• Use of multi-boot setups, which allow users to have more than one operating system on a single computer. For example, one could install Linux, BSD, Mac OS X, Microsoft Windows or other operating systems on different partitions of the same HDD and have a choice of booting into any compatible operating system at power-up.
• Protecting or isolating files, to make it easier to recover a corrupted file system or operating system installation. If one partition is corrupted, other file systems may not be affected.
• Raising overall computer performance on systems where smaller file systems are more efficient. For instance, large HDDs with only one NTFS file system typically have a very large sequentially accessed Master File Table (MFT) and it generally takes more time to read this MFT than the smaller MFTs of smaller partitions.
• "Short Stroking", which aims to minimize performance-eating head repositioning delays by reducing the number of tracks used per HDD.^[4] The basic idea is that you make one partition approx. 20-25% of the total size of the drive. This partition is expected to: occupy the outer tracks of the HDD, and offer more than double the throughput — less than half the access time. If you limit capacity with short stroking, the minimum throughput stays much closer to the maximum. This technique, however, is not related to creating multiple partitions, but generally just creating a partition less than the disk size.
  • For example, a 1 TB disk may have an access time of 12 ms at 200 IOPS (at a limited queue depth) with an average throughput of 100 MB/s. When it is partitioned to 100 GB (and the rest left unallocated) access time may be decreased to 6 ms at 300 IOPS (with a bigger queue depth) with an average throughput of 200 MB/s.
• Partitioning for significantly less than the full size available when disk space is not needed can reduce the time for diagnostic tools such as checkdisk to run or for full image backups to run.

Disadvantages of multiple partitions

Creating more than one partition has the following disadvantages, as compared to having a single partition spanning the same disk area:

• Reduces the total space available for user storage on the disk, as it forces the operating system to duplicate certain file system administration areas on the disk for each partition.
• Reduces overall disk performance on systems where data is accessed regularly and in parallel on multiple partitions, because it forces the disk's read/write head to move back and forth on the disk to access data on each partition^[5][6] and to maintain and update file system administration areas on each partition. It also prevents disk optimizers from moving all frequently accessed files closer to each other on the disk, which could reduce the number and distance of required head movements. Files can still be moved closer to each other on each partition, but those areas themselves will still be far apart on the disk. (See "short stroking" considerations above.) This issue does not apply to Solid-state drives as access times on those are neither affected by nor dependent upon relative sector positions.
• Increases disk fragmentation because it lowers the average size of continuous free blocks on each partition - as compared to a single partition of the same overall size - after the same amount of data has been written to them.
• May prevent using the whole disk capacity, because it may break free capacities apart.^[7] For example, if you have a disk with two partitions, each with 3 GB free (hence 6 GB in total), you can't copy a 4 GB DVD image file on that disk, because none of the partitions will actually provide enough space for that - even though you have more than enough free capacity in total on the disk. If the same files on those two partitions would have been stored on a single partition spanning the whole disk, then the 4 GB file could be easily stored in the 6 GB of free space.
• Hurts portability and might impose constraints on how entities might be linked together inside the file system. For example, Unix file systems and the NTFS file system allow hard links to be created only as long as both the link and the referenced file reside inside the same volume/partition.^{[8][9][10][11]} Also under Windows if you're referencing a file on another partition, you can do that only by specifying the partition's assigned drive letter (or mount point) - which, however, might change with time and depending on the drives installed. This renders references invalid and dependent on actual drive letter assignment, which is not an issue if you have to reference files/directories only on the same partition, as in this case you can use directory-relative or root-relative references, without including the drive/partition letter.