First, don't get me wrong: this is not a trial against BTRFS. I would like to see it as the best performing filesystem, as it has a ton of promising features. But hey – face the reality: its performances here were really, really low. You can argue that I used a too old kernel, or that enterprise hardware has BBU RAID cards and that it should perform much better with SSDs.
Yes, yes and yes. But older kernel are a fact of life: enterprise distributions (as RedHat, CentOS and SuSE) don't ship with bleeding-edge kernels. Moreover, spinning disks are here to stay. Finally, BTRFS itself don't like HW RAID cards so much, as they interfere with retrieving the correct data in case of bitrotting.
So, while I plan to do some test on a SSD equipped system and on a old, but enterprise-grade server, BTRFS really had to perform reasonably well in the common, 7200 RPM disks case.
In the end, while BTRFS is very well suited to manage many small, rarely-changing files (eg: fileserver, NAS), it don't bode well with large, rewriting files (as VM images and databases).
BTRFS apart, what else can we tell from this benchmark session?
Classical LVMs (preallocated volumes) remain the safer bet, performance wise. After all, they present to the guest system a mostly contiguous disk space, reducing fragmentation. On the other side, they are not very flexible: you not only have no thin provisioning options, but dealing with raw volumes is always a little clunky (eg: for backup purpose). Moreover, LVM snapshot support is quite slow. On the other hand, LVM allow for snapshotting a single volume/VM image, mitigating the snapshot performance hit. So, if you are all for the fastest build, go with normal LVM volumes.
Thin LVM are a good compromise: their default coarse chunk size (64KB to 8MB, but often in the 512KB+ range) means a less fragmented allocation than CoW filesystems, and you have the added benefit of thin storage. Moreover, thin snapshot implementation is way faster than the legacy one.
An even more interesting setup is the ThinLVM + nozeroing + filesystem combo. You take all the advantage of thin volumes (with no zeroing-imposed speed degradation) with filesystem's typical easy of use. The fastest upper filesystem to use seem to be EXT4, but even XFS remains a very good choice.
ZFS was a pleasant surprise: while it is a proven, fast filesystem under Solaris / FreeBSD, its native Linux implementation is very good (and fast). It features a load of advanced characteristics, even more that BTRFS (eg: working RAID5/6 equivalent, on-line deduplication, etc). The only complaint is that, while it is a native Linux kernel module, it is not a 100% direct porting: it is based on the Sun Porting Layer, a port providing emulation of many Solaris specific APIs. This, in turn, means that it is not possibile to include ZFS support directly into mainline kernel. Anyway, if you plan to use ZFS, remember to enable xattr=sa and to use the latest RPM/DEB version provided by the project, as older version had some rare, but nasty, bugs.