btrfs – probably not ready yet

Every time I have a conversation on SSD, someone mentions btrfs filesystem. And usually it is colored as a solution that will solve all our problems, improve overall performance and SSD in particular, and it is a saviour. Of course it caught my curiosity and I decided to perform a benchmark similar to what I did on ext4 filesystem over Intel 520 SSD.
I was prepared for surprises, as even on formatting stage, mkfs.btrfs says that filesystem is EXPERIMENTAL. In case with filesystems I kind of agree with Stewart, so question #1, what you should ask deciding on what filesystem to use, is “Was this filesystem used in a production more than 5 years?”, so from this point, btrfs has a long way ahead.

How you can get btrfs? Actually it is quite easy if you are on CentOS/RedHat/Oracle Linux 6.2.
Oracle provides Unbreakable Enterprise Kernel, which includes btrfs, so you can get it with this kernel. And installation is quite easy and straightforward, just follow instructions.

So, to numbers. Workload and benchmark are exactly the same as in my previous benchmark, and I perform runs only for 10 and 20GB buffer pool, as it is enough to understand picture. The previous run was done on ext4, so if we repeat the same on btrfs, it will allow us to compare the results.

I format btrfs with default options, and mount it with -o ssd,nobarrier options.

Throughput results:

We can see that btrfs not only provides worse throughput (5x!), but it is also less stable.

Response time:

The same happens with response time. Actually 95% response time is about 10x worse with btrfs.

And response time, timeline:

We can see that btrfs is very far from providing a stable response time.

I guess the conclusion is obvious, and I think it is fine for a filesystem that is in the EXPERIMENTAL state.
Most likely it is some bug or misconfiguration that does not allow btrfs to show all its potential.
I just will consider all talks of btrfs characteristic as premature and will wait until it is more stable
before running any more experiments with it.

Benchmarks specification, hardware, scripts and raw results are available in the full report for Intel 520 SSD.

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