Re: very slow btrfs filesystem: any data needed before I wipe it?

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Marc MERLIN posted on Sat, 12 Apr 2014 13:25:42 -0700 as excerpted:

> If I mount with ro,recovery, then it's actually normal speed to copy
> data off it, quite weird. It seems like btrfs' background processes are
> grinding the FS down to a halt, and I didn't turn on autodefrag.

What happens if you simply mount it ro, without the recovery option?  Is 
it still normal-speed or is that slow as a rw mount?

Speed hasn't been an issue here, but FWIW I normally keep my rootfs ro 
mounted as I decided that's lower risk in the event of a system crash or 
power outage and I don't actually /need/ it rw most of the time (I have a 
dedicated /var/log, /home on an entirely separate btrfs, and the bits of 
/var that need to be writable in normal operation symlinked into
/home/var/), only mounting the rootfs rw to update or do other system 
maintenance.

If a ro filesystem is normal speed but rw slow, the problem must be in 
the write path, which is what I suspect.  If a ro filesystem is slow and 
only a recover,ro filesystem is fast, then there's something strange 
going on with btrfs internals that recovery obviously bypasses.  Knowing 
one way or the other should definitely help to pin things down.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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