Editing File system (section)

=== Multiple file systems within a single system ===

Frequently, retail systems are configured with a single file system occupying the entire [[Computer storage device|storage device]].

Another approach is to [[Disk partitioning|partition]] the disk so that several file systems with different attributes can be used. One file system, for use as browser cache or email storage, might be configured with a small allocation size. This keeps the activity of creating and deleting files typical of browser activity in a narrow area of the disk where it will not interfere with other file allocations. Another partition might be created for the storage of audio or video files with a relatively large block size. Yet another may normally be set ''read-only'' and only periodically be set writable. Some file systems, such as [[ZFS]] and [[APFS]], support multiple file systems sharing a common pool of free blocks, supporting several file systems with different attributes without having to reserved a fixed amount of space for each file system.<ref>{{cite web|url=https://docs.freebsd.org/en/books/handbook/zfs/|title=Chapter 22. The Z File System (ZFS)|work=The FreeBSD Handbook|quote=Pooled storage: adding physical storage devices to a pool, and allocating storage space from that shared pool. Space is available to all file systems and volumes, and increases by adding new storage devices to the pool.}}</ref><ref>{{cite web|url=https://daisydiskapp.com/guide/4/en/APFS/|title=About Apple File System (APFS)|work=DaisyDisk User Guide|quote=APFS introduces space sharing between volumes. In APFS, every physical disk is a container that can have multiple volumes inside, which share the same pool of free space.}}</ref>

A third approach, which is mostly used in cloud systems, is to use "[[disk image]]s" to house additional file systems, with the same attributes or not, within another (host) file system as a file. A common example is virtualization: one user can run an experimental Linux distribution (using the [[ext4]] file system) in a virtual machine under his/her production Windows environment (using [[NTFS]]). The ext4 file system resides in a disk image, which is treated as a file (or multiple files, depending on the [[hypervisor]] and settings) in the NTFS host file system.

Having multiple file systems on a single system has the additional benefit that in the event of a corruption of a single file system, the remaining file systems will frequently still be intact. This includes virus destruction of the ''system'' file system or even a system that will not boot. File system utilities which require dedicated access can be effectively completed piecemeal. In addition, [[defragmentation]] may be more effective. Several system maintenance utilities, such as virus scans and backups, can also be processed in segments. For example, it is not necessary to backup the file system containing videos along with all the other files if none have been added since the last backup. As for the image files, one can easily "spin off" differential images which contain only "new" data written to the master (original) image. Differential images can be used for both safety concerns (as a "disposable" system - can be quickly restored if destroyed or contaminated by a virus, as the old image can be removed and a new image can be created in matter of seconds, even without automated procedures) and quick virtual machine deployment (since the differential images can be quickly spawned using a script in batches).