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scsichen
n00b
Joined: 10 Jun 2014
Posts: 9
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 Posted: Mon Nov 10, 2014 4:42 pm Post subject: [Solved]Is need fstrim to all subvolume of btrfs on SSD |
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I install gentoo on an SSD and use btrfs, pls see below
| Code: | mount |grep btrfs|grep rootlv
cat /etc/fstab |grep btrfs|grep rootlv
/dev/ssdvg/rootlv / btrfs defaults,noatime,compress=lzo,ssd,nobarrier,space_cache,subvol=root 0 0
/dev/ssdvg/rootlv /home/scsi/usr btrfs defaults,noatime,compress=lzo,ssd,nobarrier,space_cache,subvol=scsissd/usr 0 0
/dev/ssdvg/rootlv /home/scsi/vm btrfs defaults,noatime,compress=lzo,ssd,nobarrier,nodatacow,space_cache,subvol=scsissd/vm 0 0
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I decide use fstrim instead of mout with discard
when I fstrim on them, they all return same size
| Code: | for fs in / /home/scsi/usr /home/scsi/usr ; do fstrim -v $fs; done
/: 3 GiB (3189985280 bytes) trimmed
/home/scsi/usr: 3 GiB (3189985280 bytes) trimmed
/home/scsi/usr: 3 GiB (3189985280 bytes) trimmed |
Should I need to trim all subvolume or just trim one of them?
another quesion is every time i fstrim btrfs mount point. They alway return same size and never to zero
| Code: | su:acernb ~ # fstrim -v /
/: 3 GiB (3189985280 bytes) trimmed
su:acernb ~ # fstrim -v /
/: 3 GiB (3189985280 bytes) trimmed |
but on ext4. after fstrim, it can reach zero.
| Code: | su:acernb bin # fstrim -v /boot
/boot: 91 MiB (95364096 bytes) trimmed
su:acernb bin # fstrim -v /boot
/boot: 0 B (0 bytes) trimmed |
How can I fix it?
thank a lot
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scsi
Last edited by scsichen on Tue Nov 11, 2014 2:22 am; edited 1 time in total |
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Ant P.
Watchman
Joined: 18 Apr 2009
Posts: 6920
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| Posted: Mon Nov 10, 2014 7:17 pm Post subject: |
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The btrfs numbers are all equal between subvolumes because they share the same storage area. Think of it like a chroot.
You should only need to run fstrim once per physical device, not per logical filesystem.
Not sure about the last question, the fstrim manpage says btrfs's unchanging output for -v is expected though. ext4 may be doing something more clever. |
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scsichen
n00b
Joined: 10 Jun 2014
Posts: 9
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| Posted: Tue Nov 11, 2014 1:58 am Post subject: |
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| Ant P. wrote: | The btrfs numbers are all equal between subvolumes because they share the same storage area. Think of it like a chroot.
You should only need to run fstrim once per physical device, not per logical filesystem.
Not sure about the last question, the fstrim manpage says btrfs's unchanging output for -v is expected though. ext4 may be doing something more clever. |
Thank you for your answer. It's help a lot for me 
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