[gentoo-user] Btrfs: how to fix slow sequential write performance?

[Marc Stürmer]

Greetings fellow Gentooistas,

at the moment I am doing some testing and evaluating of Btrfs on my own 
system. Why? Just because I can and I am curious about it.

Because I am doing that for evaluation purpose please don't give advise 
like "go ZFS" or something like that, thank you.

Kernel is 3.10.7, the file system is on one hard drive only (SATA).

And here comes my question: sequential write access seems to be slow as 
hell, actually something around like 10 Mbyte/s according to dd's output.

The same HDD performed under ext4 with around 90 Mbyte/s.

Command is something like: dd if=/dev/zero of=file.img bs=1G count=150

Nothing else is running at the time of writing, no scrub/balance on the 
file system or other process eating up much cpu time.

Mount option is "relatime" only. So is this a well known issue only with 
this kernel or generally with this file system at the moment?

Are there any possible fixes to squeeze better performance out of it or 
is this unlikely to happen so that I should better take that into 
account of my evaluation and maybe dump it then?

Thanks in advance.