Storage

drive

block device: block sizes are most commonly 512 or 4096 (4K) bytes but other values are possible; all reads and writes are performed on whole blocks; LBA (logical block addressing) has replaced cylinder-head-sector addressing
Linux device names: SATA, USB, and SCSI drives: sda, sdb, ...; NVMe drives: nvme0n1, nvme1n1, ...(n is namespace)
FreeBSD device names: SATA drives: ada0, ada1, ...; USB and SCSI drives: da0, da1, ...; NVMe drives: nvd0, nvd1, ...

set of consecutive blocks on a drive
GPT (GUID partition table): 64-bit block address (nearly unlimited partition size and number of partitions); partitions have type, unique ID, attributes, name
MBR (Master Boot Record) partition table: legacy from IBM PC hard disk; 32-bit block address (partitions limited to 2TB with 512-byte blocks)
Linux device names: sda1, sda2, nvme0n1p1, nvme0n1p2, ...
Linux tools: gfdisk: GPT partitions, line interface; cgdisk: GPT partitions, curses (full screen) interface; fdisk: MBR partitions, line interface; cfdisk: MBR partitions, curses (full screen) interface; parted: GPT or MBR partitions, subcommands
FreeBSD device names: ada0p1, ada0p2, da0p1, da0p2, nvd0p1, nvd0p2, ...
FreeBSD tools: gpart: GPT or MBR partitions, subcommands; By default FreeBSD puts all filesystems in one partition called the BSD slice

set of drives or partitions or extents (finer divisions): may be created by a volume manager or an advanced filesystem; each volume has a device name, details vary
Linux tools: lvm and related commands (logical volume manager)
FreeBSD tools: zpool (part of ZFS filesystem)

set of drives or partitions or volumes combined for better performance and/or reliability
levels: RAID0: striped, data spread over multiple drives for speed, 2 or more components; RAID1: mirror, data duplicated over multiple drives for reliability, 2 or more components; RAID5: striped with parity for speed and reliability, 3 or more components; RAID6: striped with dual parity for speed and reliability, 4 or more components; RAID10: nested, RAID0 of RAID1 arrays for speed and reliability, 4 or more components; other levels are less common
Linux device names: md0, md1, ...
Linux tools: mdadm (multiple device administration)
FreeBSD tools: zpool (part of ZFS filesystem)

mount: attaches a filesystem to a (usually empty) node on the directory tree
umount: detaches a filesystem from the directory tree
/etc/fstab: file which describes filesystems (device, mount point, type, options, dump frequency, check pass)
fsck: checks for errors and (sometimes) repairs; often a wrapper which runs a filesystem-specific program; startup scripts usually do this periodically and on filesystems which were not unmounted cleanly
zfs: multi-purpose command for ZFS filesystems
other: many tools for tuning, resizing, etc.

space: a full filesystem (especially /) will cause all sorts of problems, 80% is a reasonable maximum; data will not spill from one filesystem to another so space must be planned
purpose: / (root): kernel, configuration, core utilities, booting, maintenance, everything not mounted elsewhere; /usr: utilities, applications, libraries, docs, source, etc. (all static); /var: mail, news, logs, spool files, etc. (all dynamic); /home: user home directories; /tmp: temporary files (newer systems use a pseudo-filesystem in RAM); Linux applications sometimes install in /opt, may need a separate filesystem; BSD applications often install in /usr/local, may need a separate filesystem; server data may be in /var or may need a separate filesystem

advanced filesystem developed at Sun: open source but CDDL licence not compatible with Linux GPL license; standard on FreeBSD, available for Linux but not merged into Linux kernel; Linux alternatives btrfs and bcachefs are not complete
features: large data (2⁶⁴ byte files, 2¹²⁸ byte volumes); copy on write (modified data written to another location) for integrity; checksums on data and metadata for reliability; includes volume management and RAID; flexible allocation of space to datatasets (filesystems) in pools (volumes); compression; snapshots and replication; caching; deduplication; encryption