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ZFS, the Last Word in File Systems?
guigouz writes "Sun is carrying a feature story about its new ZFS File System - ZFS, the dynamic new file system in Sun's Solaris 10 Operating System (Solaris OS), will make you forget everything you thought you knew about file systems. ZFS will be available on all Solaris 10 OS-supported platforms, and all existing applications will run with it. Moreover, ZFS complements Sun's storage management portfolio, including the Sun StorEdge QFS software, which is ideal for sharing business data."
Yes, it does look like it would be open-sourced as part of Solaris 10 (it was mentioned as one of the major new features).
Assuming the Solaris 10 will be true open source (not like Microsoft's "shared source"), as well as GPL compatibile, would I be able to use ZFS on my GNU/Linux desktop? Will ZFS be a viable alternative to ext3 and ReiserFS? Or is the overhead too big?
I was in a chat session with their engineers yesterday. It looks like they have adaptive disk scheduling algorithms to balance the load across the drives (e.g. if a drive is faster than others, it will get correspondingly more I/O). The scheduler also tries to balance I/O among processes and filesystems sharing the data pool.
This is a good thing - queueing theory shows a single unified pool has better performance than several smaller ones. People who try to tune databases by dedicating drives to redo logs don't usually realize what they are doing is counterproductive - they optimize locally for one area, at the expense of global throughput for the entire system.
ZFS uses copy-on-write (a modified block is written wherever the disk head happens to be, not where the old one used to be). This means writes are sequential (as with all journaled filesystems) and also since the old block is still on disk (until it is garbage collected) this gives the ability to take snapshots, something that is vital for making coherent backups now that nightly maintenance windows are mostly history. This also leads to file fragmentation so enough RAM to have a good buffer cache helps.
Because the scheduler works best if it has full visibility of every physical disk, rather than dealing with an abstract LUN on a hardware RAID, they actually recommend ZFS be hosted on a JBOD array (just a bunch of disks, no RAID) and have the RAID be done in software by ZFS. Since the RAID is integrated with the filesystem, they have the scope for optimizations that is not available if you have a filesystem trying to optimize on one side and a RAID controller (or separate LVM software) on the other side. Network Applicance does something like this with their WAFL network filesystem to offer decent performance despite the overhead of NFS.
With modern, fast CPUs, software RAID can easily outperform hardware RAID. It is quite common for optimizations like hardware RAID made at a certain time to become counterproductive as technology advances and the assumptions behind the premature optimization are no longer valid. A long time ago, IBM offloaded some database access code in its mainframe disk controllers. It used to be a speed boost, but as the mainframe CPU speeds improved (and the feature was retained for backward compatibility), it ended up being 10 times slower than the alternative approach.