TRIM/fstrim notes

fstrim.txt

The TRIM command enables an operating system to notify the SSD of pages which no longer contain valid data. For a file deletion operation, the operating system will mark the files sectors as free for new data, then send a TRIM command to the SSD. After trimming, the SSD will not preserve any contents of the block when writing new data to a page of flash memory, resulting in less write amplification (fewer writes), higher write throughput (no need for a read-erase-modify sequence), thus increasing drive life.

Different SSDs implement the command somewhat differently, so performance can vary.[3][8]

Trim tells the SSD to mark a LBA region as invalid and subsequent reads on the region will not return any meaningful data. However, the data could still reside on the flash internally.


are my disks TRIM enabled

lsblk -o MOUNTPOINT,DISC-MAX,FSTYPE
MOUNTPOINT DISC-MAX FSTYPE
                16M
/boot           16M xfs
                16M LVM2_member
/               16M xfs
[SWAP]          16M swap
/disks/sdb      16M ext4
/disks/sdc      16M ext4
/disks/sdd      16M ext4
/disks/sde      16M ext4
/disks/sdf      16M ext4
/disks/sdg      16M ext4
/disks/sdh      16M ext4
/disks/sdi      16M ext4
/disks/sdj      16M ext4
/disks/sdk      16M ext4
/disks/sdl      16M ext4
/disks/sdm      16M ext4

[root@dn10 system]# for i in [a-z] ; do lsblk -D  /dev/sd$i; done
NAME        DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sda                0      512B      16M         0
+-sda1             0      512B      16M         0
+-sda2             0      512B      16M         0
  +-cl-root        0      512B      16M         0
  +-cl-swap        0      512B      16M         0
sdb                0      512B      16M         0
sdc                0      512B      16M         0
sdd                0      512B      16M         0
sde                0      512B      16M         0
sdf                0      512B      16M         0
sdg                0      512B      16M         0
sdh                0      512B      16M         0
sdi                0      512B      16M         0
sdj                0      512B      16M         0
sdk                0      512B      16M         0
sdl                0      512B      16M         0
sdm                0      512B      16M         0

check the values of DISC-GRAN and DISC-MAX columns. Non-zero values indicate TRIM support.

enabling on centos7 via systemd


[root@dn10 system]# more fstrim.timer
[Unit]
Description=Discard unused blocks once a week
Documentation=man:fstrim

[Timer]
OnCalendar=weekly
AccuracySec=1h
Persistent=true

[Install]
WantedBy=multi-user.target

[root@dn10 system]# more fstrim.service
[Unit]
Description=Discard unused blocks

[Service]
Type=oneshot
ExecStart=/usr/sbin/fstrim -a



systemctl enable fstrim.timer
systemctl start fstrim.timer


by hand on the cli

[root@dn10 system]# /usr/sbin/fstrim -av
/boot: 861.4 MiB (903200768 bytes) trimmed
/disks/sdk: 84.3 GiB (90486259712 bytes) trimmed
/disks/sdi: 82.9 GiB (88970567680 bytes) trimmed
/disks/sdm: 85.3 GiB (91569057792 bytes) trimmed
/disks/sdf: 83.5 GiB (89609076736 bytes) trimmed
/disks/sdl: 84.9 GiB (91091161088 bytes) trimmed
/disks/sde: 25.1 GiB (26988478464 bytes) trimmed
/disks/sdc: 25.3 GiB (27198820352 bytes) trimmed
/disks/sdh: 83.1 GiB (89224007680 bytes) trimmed
/disks/sdj: 84.7 GiB (90879746048 bytes) trimmed
/disks/sdg: 85.9 GiB (92172173312 bytes) trimmed
/disks/sdd: 25.5 GiB (27388055552 bytes) trimmed
/disks/sdb: 25.5 GiB (27326164992 bytes) trimmed
/: 29.3 GiB (31431467008 bytes) trimmed