How to make BTRFS crawl

["Swâmi Petaramesh" <swami@petaramesh.org>]

Hi,

I was asked about situations "use cases" that would cause BTRFS to slow down 
to a crawl.

And it's exactly what happened to me yesterday when I was trying, on the 
contrary, to speed it up.

So here's the recipe for getting a "slow to the point it is unusable" BTRFS.


1/ Perform a clean, fresh install of a recent distro with a 3.13 kernel (i.e. 
Fedora 20) and a BTRFS root filesystem.

2/ Choose the version with a KDE interface

3/ Configure fstab mountpoints using such options (space_cache will have been 
manually activated once):

/ btrfs   subvol=FEDORA,noatime,compress=lzo,autodefrag

/home btrfs   subvol=HOME,noatime,compress=lzo,autodefrag


4/ Use "chattr +C" to make the following directories NOCOW (move the old 
directory elsewhere, create a new dir, make it nocow, copy files from the old 
one so they are recreated with nocow, check permissions...):

- /home/yourself/.cache
- /home/yourself/.local/share/akonadi

5/ Use IMAP mail in Kmail. Seriously process your email (it will be stored 
using akonadi mysql)

6/ Surf normally the web using Firefox

7/ Install SuSE "snapper" package that will perform a FS snapshot every hour. 
Configure it so it will snapshot both the root FS subvol and the /home subvol

8/ Use the system for 24 hours and you will know that "hardly usable" means... 
Especially every hour-on-the-hour when Kmail or Firefox will try to access 
files that have been recently snapshotted... Your system will be dead with 
saturated HD access for several *minutes*

...Hope this may help hunting this down...

Kind regards.

-- 
Swâmi Petaramesh <swami@petaramesh.org> http://petaramesh.org PGP 9076E32E