1. A Primer for Beginners
Paul W. Frields
Presented by
Red Hat, Inc.
Licensed under a Creative Commons Attribution-ShareAlike (BY-SA) 3.0 license. http://creativecommons.org/by-sa/3.0/
Linux File Systems
2. Today's Topics
Disks and partitions
Logical Volume Management (LVM)
File system formats
Concentration is on practical use by
home/desktop users
4. What kind of disks?
SATA – most laptops and home desktops)
IDE, SCSI – mainly outdated
Fibre Channel, Infiniband, and others – high
end
In most cases, your hard disk is probably the
device node /dev/sda
5. RAID
Redundant Array of Inexpensive Disks
Combine two or more disks into a group that is
managed together
Sacrifices storage capacity for fault tolerance
Avoid for today – this is an hour on its own!
6. What are partitions?
Divide your disk into usable areas
A map/table at the top describes the layout
In complex setups (>4 partitions), it becomes a
linked list
Most dual-boot systems fall into this category
Each successive table points to another table
further down the disk, and so on...
7. You need three
/boot – used to bootstrap the GRUB loader
and kernel
swap – used by the kernel to shift older data
out of RAM when memory gets tight
/ (also called “root”) – everything else can be
stored here
8. Everything in root?
Linux does not have a C: drive, D: drive...
Everything is unified under top level / folder
Under this, /bin, /etc, /var, etc.
How you break up file systems under this is up
to you – let’s look at reasons for and against...
9. Why break things up?
Guard against “out of space” problems that
might affect the running system
Lets you re-install OS without touching data (try
that on Windows with just a C: drive!)
10. Why not?
Complexity of understanding partitions
Complexity of management
Figuring out where you ran out of space
Figuring out where you need more space
“But, I have a 640 GB drive, it can’t be full!”
12. Installer defaults
Depends on the Linux distro
Most installers pick a good default
DON’T worry about it if you don’t have to
DO note the layout so you can understand
implications
14. LVM
Logical Volume Management
Turns storage into areas that can be flexibly
adjusted after the fact
Don’t use this for /boot or swap
Some installers use by default
Generally a good idea since you may want to
reallocate space later
Adds a level of abstraction (complexity)
15. LVM concepts
PV (physical volume) – a partition or disk that’s
been added to the LVM pool
VG (volume group) – one or more PVs
connected under a single name and managed
together
LV (logical volume) – a portion of a VG which is
formatted with a file system (like a partition
would be)
18. LVM system files
Boot time use of LVM defined in /etc/lvm
directory
/etc/lvm/lvm.conf – general configuration
/etc/lvm/backup/vg_name – backup of VG
definition (sizes, locations) – CAREFUL!
/etc/lvm/archive – stores previous
definitions of VGs
20. Formatted file systems
Live on a partition or LVM logical volume (LV)
Provide orderly arrangement of files
Usually hierarchical (folders, subfolders)
Store file data and metadata (timestamps,
security details, size, etc.)
Examples are ext3fs, ext4fs, btrfs, NTFS, FAT
varieties
21. Linux and other OS’s
Linux reads and writes most other OS file
systems “out of the box”
The opposite is not necessarily true!
You can get drivers for Linux file systems for
Windows, MacOS
22. FAT and NTFS
Used primarily by Windows
Also removable media where manufacturer
can’t guess your OS (85-90% case)
NTFS is needed for larger storage (>4 GB)
23. HFS+ and beyond
Apple MacOS
Older HFS is quite rare nowadays but still
supported in Linux (moving to reaonly)
24. ext3 and ext4
Standard Linux file systems
Older ext2 not used as much anymore although
it’s basically compatible with ext3
ext3 added journaling capability
ext4 supports much larger file systems
25. What is btrfs?
Pronounced “better” or “butter eff ess”
Uses more modern file system design similar to
e.g. XFS to achieve higher levels of scalability
and performance for modern workloads
Still adding features and stability
Chances are you won’t need to decide to use;
your distro will pick if/when necessary
26. File system utilities
Show disk free space (df)
Show disk usage by files (du)
Make a file system (mkfs)
File system check/repair (fsck)
Mount/unmount file system (mount/umount)
The mount utility also shows curent mounts
27. Mounts
All separate formatted file systems, when
mounted, are part of the single hierarchy
A file system can be mounted on any directory
as a mount point
System defined mounts (used at boot) in the
/etc/fstab file
29. Summary
Disks can be divided up into partitions
Partitions can be combined and split into LVM
storage
Partitions or LVM logical volumes are mounted
on the system to store files
