Slow access to btrfs on LVM/

btrfslvm

We have this setup on our server:

Ubuntu 14.04 (used to be 12.04)
10TB RAID-6 system
LVM (one VG, two LV)
ext4 partition ( ~2TB)
Btrfs partition ( ~8TB)

After a reboot last month the system was slow. First we thought it was because the RAID was resyncing (one drive was not added and was reactivated). But after that finally finished (12-13 days) access to Btrfs still is noticably slow. ext4 access seems normal.

The sysadmin who set this up (and who left this summer) already used autodefrag,noatime on the Btrfs mount.

What can we do to get Btrfs speed up again?

Best Answer

I can't comment, sorry if this is not good as answer. You should check your drives. I think 12 days of rsync time for 10Tb is too long, should be more like 12-24 hours. Look at the different drives with smartctl to check if one has many errors:

for i in a b c d e f g h i j k l; do echo $i ; smartctl -x /dev/sd$i | grep occurred | head -1 ; done

I have seen working RAID slow down because of this. And IIRC Btrfs needs more disc access than ext4 for directory look ups, which could explain access speed difference.

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Linux – Should a laptop user switch from ext4 to btrfs

I agree with vonbrand, btrfs is not yet to the maturity level of ext* or XFS or JFS to name a few. I would not use it on a laptop with precious data unless I have a reliable backup that can be done also on the go.

Btrfs can detect corruptions but it won't do anything more than reporting the detection unless you have an available uncorrupted copy of the same data, which means you either need RAID or duplication of data on the volume.

That said, I am considering using it (using RAID-1) for one machine, but I also do have Crashplan running on this machine!

For a long time, I have been using JFS on my laptop. One reason was the lower CPU usage compare to XFS or ext3 when doing file operations. I have never verified if it saved power consumption as well, but that was my assumption. I found JFS pretty stable and safe, never lost data while using it.

LVM: is this mirrored? is copy this slow

if you are creating a lvm mirror volume from zero of some TB, maybe you can use the option --nosync

man lvcreate
 Specifying the optional argument --nosync will cause the creation of the mirror to skip the initial resynchronization.  Any data written afterwards  will  be
          mirrored,  but  the  original  contents  will  not be copied.  This is useful for skipping a potentially long and resource intensive initial sync of an empty
          device.

Best Answer

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