High IO-Wait and lags under Linux after wiping SSD
I was experiencing high IO-Wait after moving a PC from Windows to Linux.
According the buffered reads the SATA interface wasn’t the bottleneck.
# hdparm -tT /dev/sda /dev/sda: Timing cached reads: 51936 MB in 2.00 seconds = 26022.54 MB/sec Timing buffered disk reads: 1318 MB in 3.00 seconds = 438.90 MB/sec
After thinking a while I remembered: the entire harddisk was encrypted and now fully rewritten. The SSD needed a trim to make it aware of all empty blocks!
# fstrim -av /boot/efi: 505,7 MiB (530309120 Bytes) auf /dev/sda1 getrimmt /boot: 0 B (0 Bytes) auf /dev/sda2 getrimmt /: 65 GiB (69787246592 Bytes) auf /dev/mapper/vgkubuntu-root getrimmt
During the first run it trimmed 1.8TB away!
Usually trimming is done by a systemd service (fstrim.timer) which is being run once a week. But it makes sense running it after a re-installation manually.