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Degradation of BTRFS-based system
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impact0r
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Joined: 24 Feb 2012
Posts: 63

PostPosted: Sat Mar 08, 2014 8:09 am    Post subject: Degradation of BTRFS-based system Reply with quote

Recently (a week or so back) I started having those problems on my BTRFS system

-------------
I. My setup:
-------------

systemd

SSD
/boot ext2 defaults 0 2
/ btrfs rw,noatime,compress=lzo,ssd,space_cache,autodefrag 0 0 (there is a /home subvolume mounted automatically)

HDD
/mnt/Disk_D btrfs rw,noatime,compress=zlib,autodefrag,nofail 0 0
(I disconnected it, but it changed nothing)



--------------------------
II. My problems:
--------------------------
- 1 - . During random boots (seems to be a 50/50 chance) the system won't boot, because it get's stuck on

[ OK ] Mounted Configuration File system
[ *** ] (1 of 13) A start job is running for dev-disk-by\.....

It will slowly cycle from 1 to 13, then come back to 1 to cycle again, and again, and after three times, I get this:

Timed out waiting for device dev-disk-by\...
Dependency failed for /boot
Dependency failed for Local File System

The computer freezes and I have to shut it down by holding the power button for several seconds.



- 2 - . My successful boot times extended considerably. I am using an automatic login and X start without any DM. Before, I could hardly see the login command line because it was so quickly covered by started OpenBox session. Now it lingers several seconds while the disk LED is working hard.



- 3 - . For the first 10-15 seconds after getting into OpenBox the heaviest processes displayed by Conky are several instances of kworker. Also, it runs heavily every time I start some program that has not been previously preloaded, making the system slugish.


--------------------------
III. Recent changes to the system:
--------------------------
Perhaps they could indicate potential suspects:

- upgraded kernel (now 3.13.5-2)
- upgraded btrfs tools (always using latest David Sterba's unstable 'integration' branch)
- did "btrfs balance /" because it had write erros due to no space even though there was like 30GB free. After doing it, no space problem went away



Does anyone have any idea what could be happening?
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gienah
Developer
Developer


Joined: 24 Nov 2010
Posts: 211
Location: AU

PostPosted: Mon Mar 10, 2014 1:05 am    Post subject: Reply with quote

I have no idea, but have this thought/guess: maybe the boot could have changed such that
the dev-disk-by ids are no longer created early enough in the boot sequence when
it is trying to use them, in which case, you could try changing to the /dev/sdXN disk devices.
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impact0r
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Joined: 24 Feb 2012
Posts: 63

PostPosted: Mon Mar 10, 2014 8:39 am    Post subject: Reply with quote

Thanks for the suggestion, but it's not it.

I did some r/w tests and the performance dropped to less than 8% of norm.


Before:
Code:
# dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 1.57307 s, 683 MB/s


Now:
Code:

# dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 26.4373 s, 40.6 MB/s



I created a new btrfs partition on the SSD with the same mount options and it is not being affected:

Code:
# dd if=/mnt/er/tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 1.57634 s, 681 MB/s



I also did
Code:
btrfs filesystem balance start /

with no effect.

This failing partition is inside LUKS container, but I also tested another LUKS container on HDD, and it had no issues, so I doubt it's dm-crypt related.
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