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Linux - Storage: Filesystem

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Linux - Storage: Filesystem
- Filesystem
- Swap

Filesystem

filesystem
- a structure used to organize and store data on storage devices.
- a logical container that stores files and directories
- created in logical volume, or Stratis pool
During OS installation, only two file systems are created in the default disk layout
- and are required for installation and booting.
- /
- /boot
Storing disparate data in distinct file systems versus storing all data in a single file system:
- Make any file system accessible (mount) or inaccessible (unmount) to users independent of other file systems.
  - This hides or reveals information contained in that file system.
- Perform file system repair activities on individual file systems
- Keep dissimilar data in separate file systems
- Optimize or tune each file system independently
- Grow or shrink a file system independent of other file systems
3 basic groups of file systems
- disk-based file systems
  - created on physical drives using SATA, USB, Fibre Channel, and other technologies
  - store information persistently
- networkbased file systems
  - disk-based file systems shared over the network for remote access.
  - store information persistently
- memory-based file systems
  - virtual;
  - they are created at system startup and destroyed when the system goes down.
  - data is not persistently saved.

`mount` Command

mount point
- a desired attachment point at which a file system connected to the direcotry structure
- any empty directory
- e.g.,/, /boot
A mount point should be empty when an attempt is made to mount a file system on it,
- otherwise the content of the mount point will hide.
As well, the mount point must not be in use or the mount attempt will fail.
options

Option	Description
`acl`/`noacl`	Enables/disables the support for ACLs
`auto`/`noauto`	Mounts (does not mount) the file system when the -a option is specified
`defaults`	Mounts a file system with all the default values (async, auto, rw, etc.)
`_netdev`	Used for a file system that requires network connectivity in place before it can be mounted.
`remount`	Remounts an already mounted file system to enable or disable an option
`ro (rw)`	Mounts a file system read-only (read/write)

Configure File: `/etc/fstab`

/etc/fstab
- A configuration file that defines how and where partitions, devices, and remote filesystems should be mounted at system boot or manually.
  - Automates the mounting of filesystems at boot.
  - Provides a convenient way to manually mount filesystems without specifying detailed options.
Structure
- Each line represents a filesystem and its mount configuration

Field	Description
`Device`	The block device or remote filesystem.
`Mount Point`	The directory where the filesystem will be mounted.
`Filesystem Type`	The type of filesystem (e.g., ext4, xfs, vfat, nfs).
`Options`	Mount options (e.g., defaults, ro, noexec).
`Dump`	Backup utility flag: 0 to skip dump or 1 to include.
`Pass`	Filesystem check order during boot (0 to skip, 1 for root, 2 for others).

Example

# Device          Mount Point     FS Type     Options         Dump   Pass
/dev/sda1         /               ext4        defaults        1      1
/dev/sda2         /home           ext4        defaults        1      2
UUID=abc123       /mnt/storage    xfs         noatime         0      2

Common Mount Options
- defaults: Default options (rw, suid, dev, exec, auto, nouser, and async).
- ro: Read-only.
- noatime: Prevents updating file access times.
- noexec: Prevents execution of binaries on this partition.
- user: Allows non-root users to mount.
RHEL attempts to mount all file systems listed in the /etc/fstab file at reboots.

Common Filesystems Types:

Filesystem types	Category	Description
`ext4`	Disk	Extended File System. Default traditional Linux filesystem.
`xfs`	Disk	Default fs in RHEL 7/8/9, supports large files, better performance.
`vfat`	Disk	Used for compatibility with Windows (FAT32).
`btrfs`	Disk	Modern filesystem with snapshot support.
`iso9660`	Disk	Used for CD/DVDs.
`swap`	Disk	Used for virtual memory (swap space).
`nfs`	Network	Network File System for remote access
`autofs`	Network	NFS file system set to mount and unmount automatically

Common Commands

General File System Commands

CMD	DESC
`blkid`	List All Block Devices with Filesystem Info
`blkid /dev/sdb1`	Display file system type and UUID.
`blkid -t UUID="uuid_number"`	Find All Devices of a Specific Filesystem Type
`blkid -t TYPE=xfs`	Find All Devices of a Specific Filesystem Type
`blkid -t LABEL="MyPartition"`	Find a Partition Using a Label
`df`	Display Disk Space Usage
`df -h`	Display Human-Readable Output
`df -h /home`	Display Disk Space where a Specific Directory locates
`df -a`	Display Space for All Filesystems
`df -i`	Display Inodes Instead of Disk Space
`df -Th`	Display Filesystem Type
`df -th ext4`	Display a specific Filesystem Type
`df -h -x tmpfs`	Exclude Certain Filesystems
`du /path/to/file`	Display Size of a File
`du /path/to/dir/`	Display Size of a Directory
`du /dir1 /dir2`	Display Size of multiple directories
`du -h /path/to/dir/`	Display Sizes in Human-Readable Format
`du -ah /path/to/dir/`	Display Size of All Files in a Directory
`du -sh /path/to/dir/`	Display Total Size of a Directory
`du -ah /path/to/dir/ \\| sort -rh`	Sort Files by Size
`du -h --exclude="*.log" /path/to/dir/`	Exclude Certain File Types
`mount`	Display all currently mounted file systems.
`mount -t ext4`	Displlay file systems with specific type
`mount fs_name mount_point`	Mount a file system to a directory.
`mount -t ext4 fs_name mount_point`	Mount with a specific file system type
`mount --move olddir newdir`	Move a mounted file system to another mount point
`umount fs_name`	Unmount a File System
`umount mount_point`	Unmount a File System

Extended File System(ext4)

CMD	DESC
`mkfs.ext4 /dev`	Creates a file system on a partition/lv.
`mkfs.ext4 -L "MyData" /dev`	Creates a file system with label.
`mkfs.ext4 -b 4096 /dev`	Creates a file system with Block Size.
`e2label /dev`	Display the current label of a partition/fs
`e2label /dev "MyPartition"`	Set a new label for an ext4 filesystem
`tune2fs -l /dev`	Tunes or displays file system attributes
`tune2fs -m 2 /dev`	Reduce reserved space to 2% (default is 5%)
`tune2fs -L "NewLabel" /dev`	Change the filesystem label
`tune2fs -U random /dev`	Change the UUID of the filesystem
`resize2fs /dev`	Extend an ext4 filesystem to use all available space
`resize2fs /dev 10G`	Resize an ext4 filesystem to 10GB

X File System(XFS)

CMD	DESC
`mkfs.xfs /dev`	Creates a file system.
`mkfs.xfs -L "MyData" /dev/sdb1`	Creates a file system with label.
`mkfs.ext4 -b 4096 /dev/sdb1`	Creates a file system with Block Size.
`xfs_info mount_point` / `xfs_info fs_name`	Display XFS Filesystem Info
`xfs_admin -l /dev/sda1`	Display XFS Filesystem Attributes
`xfs_admin -L "MyXFSData" /dev/sda1`	Set a New Label
`xfs_admin -U generate /dev/sda1`	Change the UUID
`xfs_growfs fs_name` /`xfs_growfs mount_point`	Increase XFS size
`xfs_growfs /mnt -D 500000`	Expand to a Specific Size

Swap

Physical memory(main memory)
- a finite temporary storage resource employed for loading kernel and running user programs and applications.
Swap space
- an independent region on the physical disk used for holding idle data until it is needed.
pages
- small logical chunks into which physical memory is splitted
- mapped their physical locations to virtual locations on the swap to facilitate access by system processors.
page table
- the data structure that stores the physical-to-virtual mapping of pages
- maintained by the kernel.
page out
- the process of moving selected idle pages of data from physical memory to the swap space in an effort to make room to accommodate other programs when the free memory falls below that threshold, the system starts.
page in
- return of data to the physical memory from the swap
demand paging
- entire process of paging data out and in
thrashing
- The excessive amount of paging that affects the system performance.
- When thrashing begins, the system deactivates idle processes and prevents new processes from being launched.

Prioritizing Swap Spaces

Multiple swap areas can be configured and activated to meet the workload demand.
- The default behavior of RHEL is to use the first activated swap area and move on to the next when the first one is exhausted.
The system allows us to prioritize one area over the other by adding the option “pri” to the swap entries in the fstab file.
- This flag supports a value between -2 and 32767 with -2 being the default.
- A higher value of “pri” sets a higher priority for the corresponding swap region.
- For swap areas with an identical priority, the system alternates between them。

Common Commands

CMD	DESC
`free -h`	Display Memory Usage in Human-Readable Format
`free -h -s 2`	Display Memory Continuously (Refresh Every 2 Seconds)
`free -h -s2 -c3`	Display Memory Continuously (Refresh Every 2 Seconds, repeate 3 times)
`free -m \\| grep Swap`	Display swap space
`mkswap /dev/sdb1`	Create a Swap Partition
`mkswap -L "lable_name" /dev/sdb1`	Create a Swap Partition with a label
`mkswap -c /dev/sdb1`	Create a Swap Partition and check bad blocks
`swapon`	Displays all currently active swap spaces
`swapon -a`	Enables all swap entries in the `/etc/fstab`
`swapon -p 3 /dev/sdb1`	Define a priority level for the swap space.
`swapoff /dev/sdb1`	Disable a Swap Partition
`swapoff -a`	Disable All Swap

Lab: Create SWAP

# create partition
parted /dev/sda print
# Model: ATA VMware Virtual S (scsi)
# Disk /dev/sda: 1074MB
# Sector size (logical/physical): 512B/512B
# Partition Table: gpt
# Disk Flags:

# Number  Start   End    Size   File system  Name  Flags
#  1      1049kB  512MB  511MB               main

parted /dev/sda mkpart primary 513 1024
# Information: You may need to update /etc/fstab.

parted /dev/sda print
# Model: ATA VMware Virtual S (scsi)
# Disk /dev/sda: 1074MB
# Sector size (logical/physical): 512B/512B
# Partition Table: gpt
# Disk Flags:
#
# Number  Start   End     Size   File system  Name     Flags
#  1      1049kB  512MB   511MB               main
#  2      513MB   1024MB  512MB               primary

# confirm
lsblk /dev/sda2
# NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
# sda2   8:2    0  488M  0 part

# create swap from partition
mkswap /dev/sda2
# Setting up swapspace version 1, size = 488 MiB (511700992 bytes)
# no label, UUID=8bdc174a-93e8-4abf-8771-2bcf90fcc6ab

# confirm
 lsblk -f /dev/sda2
# NAME FSTYPE FSVER LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
# sda2 swap   1           8bdc174a-93e8-4abf-8771-2bcf90fcc6ab

# add entry to fstab
echo "UUID=8bdc174a-93e8-4abf-8771-2bcf90fcc6ab swap    swap    pri=1   0   0" >> /etc/fstab

# display current swap size
swapon
# NAME      TYPE      SIZE USED PRIO
# /dev/dm-1 partition   2G   0B   -2

# activate new swap
swapon -a

# confirm
swapon
# NAME      TYPE      SIZE USED PRIO
# /dev/dm-1 partition   2G   0B   -2
# /dev/sda2 partition 488M   0B    1

free -ht
#                total        used        free      shared  buff/cache   available
# Mem:           1.7Gi       953Mi       243Mi        12Mi       716Mi       790Mi
# Swap:          2.5Gi          0B       2.5Gi
# Total:         4.2Gi       953Mi       2.7Gi

# deactivate swap
swapoff /dev/sda2

# confirm
swapon
# NAME      TYPE      SIZE USED PRIO
# /dev/dm-1 partition   2G   0B   -2

# change the priority
# deactivate swap
swapoff /dev/sda2

# change priority
swapon -p 3 /dev/sda2

# activate swap
swapon -a

# confirm
swapon
# NAME      TYPE      SIZE USED PRIO
# /dev/dm-1 partition   2G   0B   -2
# /dev/sda2 partition 205M   0B    3

Note_Tech

Linux - Storage: Filesystem

Filesystem

mount Command

Configure File: /etc/fstab

Common Filesystems Types:

Common Commands

Swap

Prioritizing Swap Spaces

Common Commands

Lab: Create SWAP

`mount` Command

Configure File: `/etc/fstab`