File systems and storage
2021-11-18
Steven Whitaker
File systems and storage
introduction
Storage:
-
Save large files like code, binary files, movies, etc.
-
HDDs, SSDs, magnetic tape
Memory:
-
Cache data
-
Any type of RAM: SRAM, SDRAM, VRAM, etc.
Swap storage is fake memory that is actually storage, but pretends to be memory. You need a partition for this, and so you typemkswap /dev/sda2 to make the partition a swap file, then swapon /dev/sdXN to enable swap. Run top or htop to see your swap and memory usage.
This talk is all about storage, not memory.
Looking at things
lsblk "list block devices", shows partitions
blkid "block device ids", shows storage UUIDs
lsblk -f gives same info as blkid
fdisk -l list all your storage media
df -h shows you the free space on each drive.
- TIP: When trying to save space, use
du -sh *to look at folder sizes and work your way down to delete the shit that's not needed.
Mounting systems
findmnt
Finds all the mounts in your system
Anything in /sys or /proc are kernel stuff. The kernel opens up files for you to look at. I don't know anything else about it! Look it up yourself, cuz I don't know what it means. It's not important to this talk.
/dev is your stuff... mostly. Here's some links to things I don't care about: /dev/pts. /dev/shm. /dev/mqueue.
Actually mounting shit
/dev/sdX are your drives! /dev/sda is your first, /dev/sdb is your second, etc.
You mount partitions.
mount /dev/sdb1 /mnt
umount /mnt
If you plug in a USB and you want to access it, use lsblk -f, then mount /dev/sdXN /mnt or wherever you want the USB files. Then, umount /mnt to safely remove.
(NOTE: if you're doing this on VirtualBox, your virtual drives have no format, so just run mkfs.ext4 /dev/sdX for every drive and you can mount them.)
Setting up the drives
fdisk /dev/sda
g sets disk as GUID Partition Table (GPT). This supports UEFI and up to 8 ZB (it goes GB, TB, PB, EB, ZB.. so a lot).
o Sets disk as a Master Boot Record MBR. This supports legacy boot, NO UEFI, and up to 2 TB size. Easier to set up than GPT.
n new partition
p primary partition (I have never used an extended partition).
w Writes what you've done
t Sets the file type. Key ones are: (MBR) 82=Linux swap, 83=Linux, fd=RAID, 8e=LVM. (GPT) 19=Linux swap, 20=Linux, 29=Linux RAID, 30=Linux LVM, 1=EFI. The default on fdisk is usually Linux.
Standard setup demo
Device Start End Sectors Size Type
/dev/sda1 2048 526335 524288 256M EFI System
/dev/sda2 526336 2623487 2097152 1G Linux swap
/dev/sda3 2623488 19400703 16777216 8G Linux filesystem
I would recommend 512M for the EFI system nowadays on Gentoo or systems that let you do this manually. Your /boot will get too clustered if you don't. I need to clean out /boot every 3rd kernel update and it can get annoying.
Logical volume management (LVM)
/---------------\ /-----\ /--------\
Logical volumes | movies | code | home |
\---------------/ \-----/ \--------/
/----------------------------------\
Volume groups | lvm |
\----------------------------------/
/----------\ /---------\ /----------\
Physical volumes | /dev/sda1 | /dev/sdb1 | /dev/sdc1 |
\----------/ \---------/ \----------/
LVM pools multiple drives together in a single logical drive and let's you split them arbitrarily afterwards.
Device Start End Sectors Size Type
/dev/sda1 2048 526335 524288 256M EFI System
/dev/sda2 526336 2623487 2097152 1G Linux swap
/dev/sda3 2623488 19400703 16777216 8G Linux LVM
/dev/sdb1 2623488 19400703 16777216 8G Linux LVM
/dev/sdc1 2623488 19400703 16777216 8G Linux LVM
Format the volume: pvcreate /dev/sdX.
View the LVM settings
pvdisplay to view physical volumes, vgdisplay to view your volume groups. lvdisplay <volume_name> to view your partitions in the volume group. This stackoverflow answer helps explain the differences and gives two good links that helped me understand what was going on, technical and practical.
Main commands
Let us assume we have /dev/sda3, /dev/sdb1/, /dev/sdc1, 3 drives ready to be added to an LVM group. We will name our volume group "lvm" because why not? This will create a folder, /dev/lvm. First, add your drives to the physical volume list:
pvcreate /dev/sda3 /dev/sdb1 /dev/sdc1
Then create a volume group with them all:
vgcreate lvm /dev/sda3 /dev/sdb1 /dev/sdc1
Say you want your home directory in a different volume:
lvcreate -L 30G lvm -n lv_home
Then use the rest of the logical volume:
lvcreate -l 100%FREE lvm -n lv_root
You got a new hard drive? Cool. It's /dev/sdd1. Add it to the volume group:
vgextend lvm /dev/sdd1
You ran out of storage in a volume group? Resize it:
lvextend -L 35G /dev/lvm/lv_home
lvreduce to drop the size. This will probably break data.
RAID
RAID is for data protection. This is not a backup. It is just for protection. Instead of one drive dying and you lose all your data, you can use a RAID system so you have protection against it dying.
Instead of a table of the different RAID systems, here's a list of them. I'm going to assume we use RAID 1 or RAID 10.
RAID is done all under mdadm. It's straightforward comapred to LVM.
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
mdadm --create /dev/md0 --level=10 --raid-devices=2 /dev/sdb1 /dev/sdc1
ZFS
You can use LVM and RAID by manually making sure you don't go over 50% or whatever RAID you want requires, then using mdadm on your logical volumes. Or just use ZFS to create a pool. Even less work.
zpool create pool /dev/sdb /dev/sdc
RAID 1:
zpool create pool mirror /dev/sdb /dev/sdc
RAID 10:
zpool create pool mirror /dev/sdb /dev/sdc mirror /dev/sdd /dev/sde
Check out what you did:
zpool status
Here is our Linux mirrors configuration:
pool: lug
state: ONLINE
config:
NAME STATE READ WRITE CKSUM
lug ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
label/lug-HGST-4TB-01 ONLINE 0 0 0
label/lug-HGST-4TB-02 ONLINE 0 0 0
mirror-1 ONLINE 0 0 0
label/lug-HGST-4TB-03 ONLINE 0 0 0
label/lug-HGST-4TB-04 ONLINE 0 0 0
mirror-2 ONLINE 0 0 0
label/lug-HGST-4TB-05 ONLINE 0 0 0
label/lug-HGST-4TB-06 ONLINE 0 0 0
mirror-3 ONLINE 0 0 0
label/lug-HGST-4TB-07 ONLINE 0 0 0
label/lug-HGST-4TB-08 ONLINE 0 0 0
mirror-4 ONLINE 0 0 0
label/lug-HGST-4TB-09 ONLINE 0 0 0
label/lug-HGST-4TB-10 ONLINE 0 0 0
errors: No known data errors
pool: zroot
state: ONLINE
scan: scrub repaired 0B in 00:01:47 with 0 errors on Sun Sep 26 16:42:05 2021
config:
NAME STATE READ WRITE CKSUM
zroot ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
da10p3 ONLINE 0 0 0
da11p3 ONLINE 0 0 0
errors: No known data errors
fstab
Automatically mount your file systems at start up and tells you which file system corresponds to which drive, etc.
<fs> <mountpoint> <type> <opts> <dump/pass>.
It is recommended you use UUIDs for non-LVM non-ZFS. It is recommended you use the device mapper symlink for LVM or ZFS. I am not smart enough to know the benefits for either.
Options are seen in "Filesystem independent mount options" and "Filesystem dependent mount options" in the mount(8) man page. I'd just use defaults. Use _netdev for a network drive (cough David cough).
The numbers at the end are not too necessary, but read the man page on the 5th and 6th fields if you really want to know. Gentoo recommends having / at 0 1 and everything else as 0 2.
```text /dev/lvm/lv_root / ext4 defaults 0 1 /dev/lvm/lv_home /home ext4 defaults 0 2 UUID=46ef4b37-b2bc-4a3a-b821-604c9fb64787 /boot ext4 defaults,noatime 0 2 UUID=61518d0a-1a81-4936-85e0-6bb7e1d69155 none swap sw 0 0