question re: trim in btrfs
Unless I'm misinterpreting something it appears that maybe btrfs doesn't pass fstrim commands down to the underlying drives when being used in a RAID-1 config.
I have this output from a small script I wrote to run at boot time (and also via cron.weekly), rather than using continous trim in the boot options:
# cat /var/log/trim.log Thu Oct 13 07:40:07 CDT 2016 /boot: 454 MiB (476062720 bytes) trimmed
Thu Oct 13 07:40:08 CDT 2016
/: 8.9 GiB (9585152000 bytes) trimmed
Thu Oct 13 07:40:22 CDT 2016
/btrfs/0: 0 B (0 bytes) trimmed
/boot and / are mdraid RAID 1 on partitions 1 and 3 of two Samsung 850 Pro SSDs. /btrfs/0 is a btrfs-raid RAID 1 of partition 4 on the same two drives. The btrfs case does not seem to accomplish anything. By comparison, I have the same drive in my laptop, but just a single one, and the non-btrfs-raid-1 file system on one of its partitions does run fstrim successfully.
This is quite possibly a known limitation, but I didn't find anything about it through some quick searching. Maybe I didn't dive deep enough...
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Forgot to mention - this was on a rather crusty 4.2.6 kernel. Just upgraded to 4.8.1 and the issue appears to have been resolved...
Quoted 25 lines · Tim
Quoted 25 lines
Unless I'm misinterpreting something it appears that maybe btrfs doesn't pass fstrim commands down to the underlying drives when being used in a RAID-1 config.
I have this output from a small script I wrote to run at boot time (and also via cron.weekly), rather than using continous trim in the boot options:
# cat
/var/log/trim.log
Thu Oct 13 07:40:07 CDT 2016
/boot: 454 MiB (476062720 bytes) trimmedThu Oct 13 07:40:08 CDT 2016
/: 8.9 GiB (9585152000 bytes) trimmedThu Oct 13 07:40:22 CDT 2016
/btrfs/0: 0 B (0 bytes) trimmed/boot and / are mdraid RAID 1 on partitions 1 and 3 of two Samsung 850 Pro SSDs. /btrfs/0 is a btrfs-raid RAID 1 of partition 4 on the same two drives. The btrfs case does not seem to accomplish anything. By comparison, I have the same drive in my laptop, but just a single one, and the non-btrfs-raid-1 file system on one of its partitions does run fstrim successfully.
This is quite possibly a known limitation, but I didn't find anything about it through some quick searching. Maybe I didn't dive deep enough...
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Quoted 6 lines
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Quoted 2 lines · Tim Walberg
Forgot to mention - this was on a rather crusty 4.2.6 kernel. Just upgraded to 4.8.1 and the issue appears to have been resolved...
Thanks for following up. This issue was actually fixed in v4.3. There were a bunch of fixes for discard ranging from correct(ish[1]) reporting of bytes discarded, discarding ranges in freed block groups, and missing discards when using -odiscard.
-Jeff
[1] We report the range for which we issue discards. We don't track if a particular range has been previously discarded.
Quoted 36 lines · Tim
Quoted 25 lines
Quoted 25 lines
Unless I'm misinterpreting something it appears that maybe btrfs doesn't pass fstrim commands down to the underlying drives when being used in a RAID-1 config.
I have this output from a small script I wrote to run at boot time (and also via cron.weekly), rather than using continous trim in the boot options:
# cat
/var/log/trim.log
Thu Oct 13 07:40:07 CDT 2016
/boot: 454 MiB (476062720 bytes) trimmedThu Oct 13 07:40:08 CDT 2016
/: 8.9 GiB (9585152000 bytes) trimmedThu Oct 13 07:40:22 CDT 2016
/btrfs/0: 0 B (0 bytes) trimmed/boot and / are mdraid RAID 1 on partitions 1 and 3 of two Samsung 850 Pro SSDs. /btrfs/0 is a btrfs-raid RAID 1 of partition 4 on the same two drives. The btrfs case does not seem to accomplish anything. By comparison, I have the same drive in my laptop, but just a single one, and the non-btrfs-raid-1 file system on one of its partitions does run fstrim successfully.
This is quite possibly a known limitation, but I didn't find anything about it through some quick searching. Maybe I didn't dive deep enough...
Quoted 6 lines
Quoted 6 lines
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[email protected], [email protected]
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To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected]
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Jeff Mahoney SUSE Labs