gedankensplitter/filesystems.md

# Filesystems
## btrfs
### btrfs scrub
As a copy-on-write (COW) filesystem btrfs can compensate some errors from the underlying storage
- check checksum on READ
- fix logical block if valid copy is available (RAID1, RADI5/&, DUP)
- 07.2022 no force WRITE-VERIFY possible -> look downwards
##### btrfs resize
```
btrfs filesystem show -d
btrfs filesystem resize -500m /dev/mapper/ubuntu--vg-root/@subvolume
```
##### btrfs snapshot size
to show all snapshots enable quotas
```
    [root@localhost ~]# btrfs quota enable /btrfs/
    [root@localhost ~]# 
    [root@localhost ~]# btrfs qgroup show  /btrfs/
```
##### systemd handling
create for all btrfs filesystems a regulary scrub timer.
```bash
for p in $(lsblk -nflo FSTYPE,MOUNTPOINT | awk '$1=="btrfs"{print $2}'); do systemctl enable --now "btrfs-scrub@$(systemd-escape -p "$p").timer"; systemctl start "btrfs-scrub@$(systemd-escape -p "$p").service"; done
```
the manual way of creating is eating the correct escape.

###

### ATA/SMART
#### hdparm
##### write-verify
with hdparm you can activate the write-verify `-R1` handling, if the drive has got this feature. Most consumer devices do not have this. Otherwise hdparm is more for the temporary set of AAM or APM, ATAsecurity, DCO, e.g. To disable use `-R0`
```
/dev/sdb: [SSD]
 multcount     =  0 (off)
 IO_support    =  1 (32-bit)
 readonly      =  0 (off)
 readahead     = 256 (on)
 geometry      = 31130/255/63, sectors = 500118192, start = 0

/dev/sda: [HDDD]
 multcount     = 16 (on)
 IO_support    =  1 (32-bit)
 readonly      =  0 (off)
 readahead     = 256 (on)
 geometry      = 60801/255/63, sectors = 976773168, start = 0
```
If it tells you `write-read-verify = 2` then the feature is enabled
#### smartmontools
the smartmontools contains mainly two features: the smart daemon and the smartctl tool. `smartctl` controls the SMART features of a drive, `smartd` usually surveille and run tests as a daemon with it.